Robust:
“Road Upgrade of Standards”
Marco Anghileri
Dipartimento di Ingegneria Aerospaziale
Politecnico di Milano
Italy.
NCHRP 22_24 Interim report Meeting.
Washington 2008-01-11
Robust
• EU FP5 sponsored three year project.
• Scope: create knowledge to improve EN-1317.
Robust. GRD1-2002-70021
• Strong integration with CEN/TC226/Wg1/Tg1.
• The project covered 3 main items (referred to
EN1317):
2
– 1 Study of the current situation.
– 2 Experimental procedures.
– 3 Computational mechanics.
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
1
Robust activities.
Study of the current situation
• To verify the relevance of 1317 on roadside
safety.
– Statistical study of real life accidents and injuries to
verify the contribution of 1317.
Robust. GRD1-2002-70021
– Verification of the correspondence between testing
procedures and real life accidents.
4
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
2
Robust activities.
Experimental procedures.
• Testing procedures.
• Vehicle influence
• Impact tolerances (velocity/angle)
• Soil influence
Robust. GRD1-2002-70021
• Instrumentation mounting
• Data acquisition.
• Data analysis.5
• Influence of software.
• Severity indices.
• Moving average
• PHD definition
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
3
Robust activities.
Computational mechanics.
• To improve the use of CM inside the certification
process.
Robust. GRD1-2002-70021
– Vehicle models improvement.
– Simulation procedures.
6
– Parametric studies.
– Validation procedures.
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
Item 1: Current situation.
• Statistical analysis of current level of safety around
Europe.
Robust. GRD1-2002-70021
–
–
–
–
Collection of data from real life accidents.
Impacts only against EN1317 safety barriers.
To investigate the application of EN1317 standards.
To verify that EN1317 testing procedures is representative of
real life.
• Incident data from:
–
–
–
–
Single vehicle incidents.
7
Incidents an ALL roads
Incidents which a VRS has been hit
Only incidents from 1° Jan 1990
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
Data collection table.
• General incident information (date, road type,
speed limit).
• Details of the vehicle (make, model, weight).
Robust. GRD1-2002-70021
• Movement and damage to the vehicle.
• Severity and location of injuries to the
occupant(s).
• Type of VRS.
8
• Impact speed and angle.
• Data source(s).
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
Current situation.
Results and recommendations
• For all impact testing with cars, an impact speed
of 110 km/h is recommended for all testing;
Robust. GRD1-2002-70021
• The impact angle for cars remains at twenty
degrees.
• The number of registered motorcycles be
reordered, and the occurrence of such incidents
analyzed in future
years.
9
• It is recommended that the weight specified for
the small car test (currently referred to as TB11)
should be changed so as to be 950 ± 50 kg;
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
Current situation.
Results and recommendations
Robust. GRD1-2002-70021
• It is recommended that the vehicles used for the
testing of VRS are no more than 5 years old;
• The data have shown that one dummy (either
instrumented or not instrumented) should be
seated in the vehicle during all testing between
cars and VRS;
• It is further recommended
that the dummy should
10
be placed on the driver’s side of the vehicle and
this should be the impact side. The dummy
should be restrained by a seat belt;
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
2
Experimental procedures.
• Testing procedures.
• Vehicle influence
• Impact tolerances (velocity/angle)
• Soil influence
Robust. GRD1-2002-70021
• Instrumentation mounting
• Data acquisition.
• Data analysis.11
• Influence of software.
• Severity indices.
• Moving average
• PHD definition
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
2 Testing procedures.
•
Scope:
– Reduce scatter between labs.
– Improve testing procedures.
– Obtain benchmarks for computational mechanics activity.
Robust. GRD1-2002-70021
•
Activities:
– Round robin activity with rigid barrier
– Round robin activity with deformable barrier
– Round robin with
12heavy vehicles.
– Same test repeated in the same test house
– Collection of procedures used during testing inside the different test
houses.
– Statistical analysis of already performed test (TB11 - 900 kg 100 km/h
20°) to investigate procedures for severity indices evaluation and
possible correlation between existing severity indices.
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
Round robin with rigid barrier
• Rigid barrier:
– Same rigid barrier
– 900 kg 100 km/h 20°
Robust. GRD1-2002-70021
– 6 tests with same new car
– 4 tests with test house
standard cars
13 with the
– 2 additional tests
same new car and
improved procedures
– In total 12 tests.
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
Round robin with rigid barrier
• Analysis of results showed and analyzed scatter from:
– Transducer mounting procedures.
– Data acquisition (example: zeroing)
– Severity indices evaluation:
• Software
• 1317 procedures
Robust. GRD1-2002-70021
– Small vehicle differences:
• Tires-ground interaction
• 2 – 4 doors
14
– Sensitivity to vibration of some severity indices (Phd,ASI).
Med
Asi
1.86
THIV 32.89
PHD 14.15
max
0.05
1.31
3.55
%
2.83
3.98
25.1
min %
-0.03 -1.48
-0.49 -1.5
-2.75 -19.4
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
Round Robin on deformable barrier.
Robust. GRD1-2002-70021
• One TB11 test in each of the test houses on the
same N2 steel barrier with the same car
15
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
Robust. GRD1-2002-70021
Round Robin on deformable barrier.
16
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
Round Robin on deformable barrier.
Robust. GRD1-2002-70021
• Scatter for these series of tests is bigger than the
scatter observed for Round Robin with rigid
barrier.
• The only difference was the use of a soft barrier
and different soils conditions.
17
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
Round Robin with heavy vehicles.
Robust. GRD1-2002-70021
• Tests with two different heavy vehicles, TB42 and
TB51, one performed identically three times and one
performed twice, to evaluate experimental result
scatter
18
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
Robust. GRD1-2002-70021
Round Robin with heavy vehicles.
19
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
Statistical analysis of existing data
• Example: Thiv-ASI correlation
Corrélation THIV/ASI
Corrélation THIV - ASI (All data)
50.00
70.00
45.00
60.00
y = 13.748x + 11.409
Robust. GRD1-2002-70021
40.00
2
R = 0.6359
50.00
35.00
THIV
THIV/ASI-All
25.00
20
20.00
15.00
VAL limites
Lineare (THIV/ASI-All)
THIV
Autostrada
30.00
40.00
LIER
..
30.00
TRL
20.00
10.00
10.00
5.00
0.00
0
0.5
1
1.5
ASI
2
2.5
3
0.00
0.00
0.50
1.00
1.50
ASI
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
2.00
2.50
3.00
Statistical analysis of existing data
• ASI-dynamic deflection correlation:
2.00
1.20
ASI-DD
Espo. (ASI-DD)
ASI
Robust. GRD1-2002-70021
1.60
0.80
21
0.40
0.00
0.00
y = 1.461e-0.688x
2
R = 0.589
0.50
1.00
1.50
2.00
Dynamic deflexion
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
Composite mounting fixing.
• Installation of accelerometers can
affect measures and severity
indices.
Robust. GRD1-2002-70021
• The weight of the mounting block
is a crucial problem
22
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
Robust. GRD1-2002-70021
Deceleration tests.
23
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
Deceleration tests. Results.
• Frequency response of impact pulses:
– Strong differences between different mounting blocks.
– Differences at frequencies where severity indices work.
spectrum power density. y direction. 70° impact
spectrum power density. y direction. 70° impact
8000
Aluminium
Composite
Robust. GRD1-2002-70021
7000
Aluminium
Composite
7000
6000
6000
24
5000
5000
4000
4000
3000
3000
2000
2000
1000
1000
0
0
0
20
NCHRP
22_24
Report meeting.
Washington
2008-01-11
40
60 Interim 80
100
2
4
6
8
10
12
14
ASI. Acceleration Severity Index
– “The index ASI is intended to give a measure of the
severity of the vehicle motion for a person seated in the
proximity of point P (CG) during an impact.”
– Steps:
• Measure three acceleration components of vehicle CG
according with CFC180.
Robust. GRD1-2002-70021
• Apply a 50 ms moving average on these acceleration.
• Evaluate Asi as:
25
2
 a   a   a 
ASI ( t )   x    y    z 


 ax lim   a y lim   az lim 
2
2
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
Moving average
• Questions:
– Can moving average distort signals?
Robust. GRD1-2002-70021
– Can moving average give wrong information?
27
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
50 ms moving average – standard
filtering gain.
• Gain=output/input
1
Butterworth filter
0.9
0.8
0.7
Gain
Robust. GRD1-2002-70021
0.6
0.5
0.4
30
0.3
0.2
0.1
0
20
40
60
freq [Hz]
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
80
100
50 ms moving average – standard
filtering attenuation.
• Attenuation.
0
100
Moving average
Filter
Moving average
50
-50
0
-100
Amplitude [Db]
Robust. GRD1-2002-70021
Amplitude [Db]
-50
-100
-150
31
-200
-150
-200
-250
-250
-300
-300
-350
-350
0
10
0
20
40
60
80
100
10
1
2
10
freq [Hz]
freq [Hz]
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
10
3
10
4
Moving average does not
preserve energy.
• Velocity evaluation with:
– Original signal
– Filtered signal (Butterworth)
– Moving Average
Velocity evaluation
Velocity evaluation
0.6
1
Robust. GRD1-2002-70021
Moving average
Original signal
Filtered signal
0.5
Moving average
Original signal
Filtered signal
0.4
0.2
32
0
-0.2
velocity
velocity
0
-0.5
-0.4
-0.6
-1
-0.8
-1
-1.5
-2
-1.2
-1.4
0
0.2
0.4
0
0.2
0.4
0.6
0.6 22_24 Interim
0.8
1
NCHRP
Report
meeting. Washington 2008-01-11time
time
0.8
1
1.2
1.4
Is this a real problem?
• To verify the presence of this problem:
– Test cases obtained from some standard crash tests.
• Acceleration time-history.
Robust. GRD1-2002-70021
– Original
– Filtered with moving average.
35
– Filtered with a “correct” filter.
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
Example.
TEST 3: accelerazione X
30
20
10
g
0
-10
TEST 3: accelerazione Z
-20
15
-30
10
-40
5
0
0.2
Robust. GRD1-2002-70021
-50
0.4
0.6
0.8
1
g
time [s]
TEST 3: accelerazione Y
0
36
20
-5
15
10
-10
g
5
-15
0
0
0.2
0.4
-5
-10
-15
-20
0
0.6
time [s]
0.2
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
0.4
0.6
time [s]
0.8
1
0.8
1
TEST 3:Confronto tra media mobile e filtraggio. Componente X
2
Media mobile
Filtro
0
-2
-4
-6
g
TEST 3:Confronto tra media mobile e filtraggio. Componente Z
3
-8
2.5
-10
-12
2
-14
1.5
-16
Media mobile
Filtro
0
0.2
0.4
0.6
0.8
1
1
g
time [s]
0.5
TEST 3:Confronto tra media mobile e filtraggio. Componente Y
Robust. GRD1-2002-70021
2.5
0
Media mobile
Filtro
2
-0.5
37
1.5
-1
1
-1.5
g
0.5
0
0.2
0.4
0.6
time [s]
0
-0.5
-1
-1.5
-2
0
0.2
0.4
0.6
0.8
1
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
time [s]
0.8
1
Moving average
• The modification of original signals driven by the
moving average has been demonstrated but:
• Is this strange behavior of moving average
desired by the original designer of ASI?
Robust. GRD1-2002-70021
• Or was simply not observed?
38
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
History of ASI.
– I.Laker: “ A short summary of three vehicle Impact Severity
Measure- ASI THIV/PHD NCHRP 230” 1991.
Robust. GRD1-2002-70021
• First step: the Shoemaker table
39
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
History
• 1955 Stapp tests.
• 1969 Limits in 3 direction from Cornell
Aeronautical Laboratories
Robust. GRD1-2002-70021
• 1971 Moving average.
• 1972 Ellipsoidal Envelope from US Air force
documents
42
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
Acceleration time histories.
– Aeronautical deceleration:
• Source: Us Army “Aircraft Crash
Survival Design Guide”.
• Single peak: from 15 to 30 g
43
– Safety barrier deceleration.
TEST 1: accelerazione X
10
5
0
g
Robust. GRD1-2002-70021
• Time duration from 0.1 to 0.15 s
-5
-10
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
-15
0
0.2
0.4
0.6
time [s]
0.8
1
ASI History
•
•
Robust. GRD1-2002-70021
•
•
•
ASI was based on research on the injury assessment of vehicle
and aircraft occupants in phenomena such as re-entry space
capsule impacts and combat airplane maneuvers.
These phenomena have limited or no oscillations throughout the
event.
For this reason, computing an average over a period of 50 ms was
used to obtain an average value to be compared with the tolerable
limits.
Impacts against road restraint systems generally have a duration
much greater than 50 milliseconds, and show strong oscillations
at different frequencies.
44
The 50 ms moving average when applied over such longer
acceleration pulses becomes a low-pass filter, but it does not
behave like filters used conventionally for crash analysis
distorting randomly the original signals.
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
Modification of ASI formulation.
• 126 tests analyzed
• Evaluation of ASI using filtering instead of moving average.
• 2 poles Butterworth forward – backward filter (to avoid time
shift). 4 total poles.
Robust. GRD1-2002-70021
• Cut off frequencies tested:
10 – 12 – 14 – 16 – 18 – 20 hz
• The final cut off frequency has been identified as the one
45
with the better correlation
with the standard ASI formula.
The idea is to avoid, if possible, modification of the current
limits for the ASI formula.
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
Filtered ASI.
• Best correlation (not in all the domain):
– 12 hz cutoff frequency.
– 2 pole forward-backward Butterworth filter. (4 resultant poles)
ASI filtered
Robust. GRD1-2002-70021
2.2
2.1
2.0
1.9
1.8
1.7
1.6
1.5
1.4
1.3
1.2
1.1
1.0
0.9
0.8
0.7
0.6
46
0.6
0.7
0.8
0.9
1.0
1.1
1.2
asi
12 hz
Lineare (asi)
Lineare (12 hz)
1.3
1.4
1.5
1.6
1.7
1.8
1.9
2.0
2.1
NCHRP 22_24 Interim
Report meeting. Washington 2008-01-11
ASI standard
2.2
Experimental activities output
• Proposal of PHD deletion. (Phd has been deleted)
Robust. GRD1-2002-70021
• Study on accelerometer mounting block (in the
revision of 1317 mounting block will be deleted
and accelerometers will be placed directly on the
tunnel).
• Study on Asi evaluation procedure. (ASI formula
has been modified
deleting the moving average).
47
• Soil must be better defined and controlled during
tests (TG1 is discussing how to measure soil
variation before tests).
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
3 Computational mechanics
• Create a vehicle data base.
• Produce information for CME group.
• Identify procedures to be used during computational
mechanics activity for certification.
Robust. GRD1-2002-70021
– Vehicle modeling.
– Soil modeling.
– Materials.
48
– Numerical data acquisition and severity indices evaluation.
• Improve the level of confidence inside computational
mechanics
• Study validation procedures.
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
Robust. GRD1-2002-70021
Vehicle data base. Robust.
49
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
Geo metro models.
• Situation:
• R0: NPRA modification of NCAC
Robust. GRD1-2002-70021
• R1: Polimi modification R0 (suspension,
meshing).
• R2: R1+seats and gebod
• R3: R1+ steering
50
• R4: R3+gebod+seats
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
Robust. GRD1-2002-70021
First modifications.
Wheel/suspension problems.
51
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
Front suspensions and steering
system
Robust. GRD1-2002-70021
• The actual Geo-Metro front suspensions are
McPherson type.
52
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
Robust. GRD1-2002-70021
Front suspensions and steering
system
• Original Geo Metro model has been strongly remeshed and than
modified adding suspension and steering.
• In the old version of the Geo-Metro FE model the two front
wheels were fixed to the respective side of the vehicle’s frame
by a deformable beam
• Each wheel cannot steer unless the beam doesn’t fail.
• These two beams increased the stiffness of the suspensions
assembly.
• Furthermore, in order to coordinate the steering movement of
front wheels, a rigid
53 link between the front rims was defined.
• Even if this link could synchronize the wheels during the
steering action, it was not quite correct because it made the
steering and suspension motion dependent: the suspension
compression or rebound made the wheels steer, too!
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
Front suspensions and steering
system
• Front suspensions of the model have been enhanced by the
redefinition of old joints and the creation of new ones which
now allow a steering capability of the vehicle.
Robust. GRD1-2002-70021
• Simple simulation have been run to check the system
54
Spindle
Lower A-arm
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
Steering system
Robust. GRD1-2002-70021
• Steering of front wheels
under the application of a
force to the right wheel
only and the vehicle raised
from the ground.
55
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
Robust. GRD1-2002-70021
Handling capabilities.
56
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
Robust. GRD1-2002-70021
57
Steering force
removed after
0.5 sec
Steering force
applied for all
the time
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
Measure of severity indices and time
histories
• The measure of severity indices and time histories requires
two important verification:
– Numerical data acquisition behavior
Robust. GRD1-2002-70021
– Numerical definition of the transducer
• The numerical data acquisition must be able to acquire
data that can reconstruct properly the physics of the
phenomenon.
• The definition of58
the transducer must be comparable to the
behavior of a typical transducer used during crash tests.
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
Output frequency influence.
•
•
•
•
Round Robin scenario. Small vehicle 100 km/h 20° rigid barrier.
Ls-dyna 970 solver 5434a version.
To verify the behaviour of the numerical data acquisition system,
accelerations have been sampled at different frequencies.
Three output frequencies were considered:
Robust. GRD1-2002-70021
• 854 kHz (sampling time equal to the integration timestep),
• 100 kHz
• 10 kHz.
•
•
The data output in the NODOUT ASCII file were used to compute the
occupant risk factors, as prescribed in the EN1317 specifications, by
means of the Test 62
Risk Assessment Program (TRAP).
The output data were initially filtered with a standard CFC180 filter and
then processed by the software.
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
Comparison.
•
•
Robust. GRD1-2002-70021
•
How can we define which is the proper acceleration and the
wrong and why an acceleration sampled during a numerical
simulation can be wrong?
Besides the acceleration time history also the velocity and
displacement time histories can be obtained from these nodes.
To understand which is the right acceleration and which is the
wrong, we must verify that:
– the velocity and the displacement obtained integrating the
acceleration
– And
63
– the velocity and displacement directly sampled.
– Must be equivalent
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
Lateral velocity comparison
1000
Vy 854kHz Sampled
Vy 854kHz Integrated
0
• 854 kHz
-1000
Velocity [mm/s]
-2000
-3000
-4000
-5000
-6000
-7000
-8000
0
0.025
0.05
0.075
Time [s]
0.1
0.125
0.15
1000
Vy 100kHz Sampled
Vy 100kHz Integrated
0
• 100 Khz
Velocity [mm/s]
-2000
-3000
-4000
64
-5000
-6000
-7000
-8000
0
0.025
0.05
0.075
0.1
0.125
0.15
2000
Vy 10kHz Sampled
Vy 10kHz Integrated
0
• 10 Khz
-2000
Velocity [mm/s]
Robust. GRD1-2002-70021
-1000
Time [s]
-4000
-6000
-8000
-10000
-12000
-14000
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
0
0.025
0.05
0.075
0.1
Time [s]
0.125
0.15
Vertical velocity comparison
4000
Vz 854kHz Sampled
Vz 854kHz Integrated
3500
3000
• 854 kHz
Velocity [mm/s]
2500
2000
1500
1000
500
0
-500
-1000
0
0.025
0.05
0.075
Time [s]
0.1
0.125
0.15
4000
Vz 100kHz Sampled
Vz 100kHz Integrated
3500
3000
Velocity [mm/s]
• 100 Khz
2000
1500
1000
500
65
0
-500
-1000
0
0.025
0.05
0.075
0.1
Time [s]
0.125
0.15
10000
Vz 10kHz Sampled
Vz 10kHz Integrated
8000
• 10 Khz
6000
Velocity [mm/s]
Robust. GRD1-2002-70021
2500
4000
2000
0
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
-2000
0
0.025
0.05
0.075
0.1
Time [s]
0.125
0.15
Comparison results.
• Acceleration sampled at 854 Khz and 100Khz are able to
reconstruct correctly the velocity and the displacement of
the vehicle.
Robust. GRD1-2002-70021
• Acceleration sampled at 10 Khz (standard sampling rate
used for experimental testing) is not able to reconstruct the
motion of the vehicle.
66
• Signals sampled at 10 Khz have problems similar to
aliasing.
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
Robust. GRD1-2002-70021
Data acquisition conclusion.
• This problem showed that numerical data acquisition has
the same typical problems of the experimental data
acquisition.
• Care must be taken for the definition of the sampling rate.
High sampling rate means huge amount of data.
• This problem is mesh sensitive and code sensitive (Pam
crash has pre-sampling filtering).
• The requirement we included in our procedure is that, to
prove the proper data acquisition, the reconstruction of the
motion must be 67
demonstrated starting from acceleration
time histories.
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
Numerical accelerometer definition.
Robust. GRD1-2002-70021
• Now that we have demonstrated the capability of
our numerical data acquisition the problem is
shifted to the transducer itself.
• This numerical transducer must be compared to
a standard real transducer. If we want to compare
these two output these transducers (numerical
and experimental) must be equivalent.
68
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
Numerical-experimental transducers.
Robust. GRD1-2002-70021
• Typical real
acceleromet
er frequency
response.
• Numerical accelerometers
are not damped. They can produce
69
frequencies up to the natural frequency of the element where
they are attached.
• We have seen how to acquire these signals but now we must
make them equivalent to the experimental ones
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
Numerical accelerometer processing
Robust. GRD1-2002-70021
– We have seen that sampling frequency must be
adequate to avoid numerical aliasing problems
(generally much higher that the experimental one).
– A new filtering (before the same filtering used during
experimental data acquisition process) must be used to
adequate the numerical frequency response to the real
frequency response.
– Which frequency?
70
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
Example applied to the Round Robin
Frequencies relevant for
Activity
severety indices evaluation
13
Spectrum
Spectrum
Spectrum
Spectrum
Spectrum
x 10
3.5 x 1012
12
x 10 12
x 10 11
12
x 10
16
3
8
4
2
14
2.5
7
2.5
3.51.8
• Round robin.
Numerical original signal
Numerical
CFC1000
Numerical
original signal
Numerical
CFC600
Numerical
CFC1000
Numerical
original signal
NumericalCFC180
Numerical
CFC600
Numerical
CFC1000
Numerical
original signal
Numerical
original signal
CFC180
Numerical
CFC60
NumericalCFC180
Numerical
CFC600
Numerical
CFC1000
Numerical
CFC1000
CFC60
Experimental
unfiltered
signal
Numerical
CFC60
NumericalCFC180
Numerical
CFC600
Numerical
Experimental
CFC600
unfiltered
Experimental
unfiltered
signal signal
Numerical
CFC60
NumericalCFC180
NumericalCFC180
Experimental
unfiltered signal
Numerical CFC60
Numerical CFC60
Experimental
unfiltered signal
Experimental unfiltered signal
• Experimental sampling rate :10 kHz
12
• Numerical
sampling rate: 100 kHz
6
1.6
3 2
10
5 1.4
2.5
amplitude
amplitude
amplitude
amplitude
amplitude
Robust. GRD1-2002-70021
2
1.5 8
4
1.2
1.5
2
1
1
6
71
3
1.50.8
1
4
2 0.6
1
0.5
2
0.4
1 0.5
0.5
0
00
0.20.5
00
00
00
0
1
2.5
3
3.5
4
4.5
5
1frequency [hz]
1.5
2
4 2.5
x 1012000
4000
6000 [hz]
8000
10000
4
frequency
x 106000
2000
3000[hz]
4000
5000
frequency
1000
500
1500 [hz]
2000
1000
2500
3000
1500
frequency
Interim Report meeting.
Washington
2008-01-11
frequency [hz]
0.5
2000
1000
500
NCHRP 22_24
1.5
2
Numerical accelerometer.
• To correctly sample acceleration time histories:
– Demonstrate that you are able to properly reconstruct
the motion (with Geo Metro R4 100 kKhz).
Robust. GRD1-2002-70021
• To correctly compare the numerical
accelerometer to the experimental one:
– Pre-filter data to have a numerical frequency response
similar to the experimental one (with Geo Metro R4
72
CFC60).
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
Parametric studies.
•
The following points have been studied to better define procedures for the
use of CM during the standardization process.
–
Friction
•
•
Robust. GRD1-2002-70021
–
Boundary conditions for the barrier
•
•
•
–
between wheel / wearing course
between barrier and vehicle
Ground condition
Anchoring of the barrier
Length of the barrier
Vehicle
•
•
•
•
•
•
•
Impact point
73
Speed of the vehicle
Weight of the vehicle
Spinning wheels
Instrumentation
Mounting Block
Location of the accelerometer
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
Other parametric studies.
• Parametric study on material properties
• ASI, THIV and Dynamic deflection variation on
– Material properties:
Robust. GRD1-2002-70021
• E-module,
• Yield stress (S235 steel has a variation of yield stress from
235 to 360 Mpa)
– Material thickness
based on % change
74
• The material properties should have an upper
and a lower limit
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
Robust. GRD1-2002-70021
Parametric study result.
75
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
Robust. GRD1-2002-70021
Parametric study result.
76
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
Validation
• Validation methods have been studied using the
benchmark cases obtained during the Round
Robin activities.
Robust. GRD1-2002-70021
• Validation has been identified not only on
severity indices value but also on time histories.
• The method to be used for validation must be
objective and77
able to validate also experimental
tests performed inside the tolerances defined by
the standards.
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
Validation based on velocity
comparison.
• Accelerometers comparison does not fit for
objective validation method.
Ay filtered at 180 hz
Autostrade
Hut
Cidaut
Lier
TRL
40
30
Robust. GRD1-2002-70021
20
• Was decided to
use a global reference frame
78
velocity comparison.
10
0
– Rotations
-10 of accelerations (unfiltered).
– Evaluation of global reference frame velocities.
-0.05
0
0.05
0.1
0.15
0.2
0.25
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
All RR tests.
• Same rigid barrier.
• Different vehicles.
• 12 tests
Vy global Unfiltered
Vx global Unfiltered
28
10
26
Robust. GRD1-2002-70021
12
8
24
79
6
22
Vz global Unfiltered
4
4
20
3
2
18
2
0
-2
-0.4
16
1
-0.2
0
0.2
0.4
0.6
0.8
1
14
-0.2
0
0
0.2
-1
-2
NCHRP 22_24 Interim
Report meeting. Washington 2008-01-11
-3
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
0.4
0.6
0.8
1
1.2
Validation based on velocity
comparison.
• To take into account the different importance of
components, validation based on resultant
velocity.
Robust. GRD1-2002-70021
• After the point where the difference between
simulated and measured resultant velocity is
greater than:
– Xx% of current velocity (suggestion:± 5% of initial
current velocity)?
80
– Xx% of initial velocity (suggestion:± 5% of initial
velocity)?
The model is no longer validated.
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
Comparison based on resultant
velocity.
reultant velocity
28
27
26
25
Robust. GRD1-2002-70021
24
23
22
81
21
20
19
18
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
Validation. All requirements.
• Severity indices:
– ASI
THIV
• Barrier behavior.
• Deformation (WW, DD).
Robust. GRD1-2002-70021
• Failures (number and location).
• Vehicle:
82
• Trajectories.
• Failures ? (during RR different failures)
• Resultant velocity.
• Yaw rate
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
Computational mechanics.
• Techniques been developed inside Robust
project have been applied to all experimental test
case (each test repeated several times):
– Rigid barrier
Robust. GRD1-2002-70021
– Deformable barrier
• Different numerical test houses.
83
• Results available
at:
http://www4.vegvesen.no/ROBUSTDOC/
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
Conclusion
• Robust produced an huge amount of results that
now can be used to revise standards.
• Regarding CM
– Benchmarks
Robust. GRD1-2002-70021
– Procedures
– Experience
Are available for84the integration of this method
inside the certification process.
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11
Robust. GRD1-2002-70021
Questions?
85
NCHRP 22_24 Interim Report meeting. Washington 2008-01-11