ISO/TS 18571:2014

TECHNICAL ISO/TS
SPECIFICATION 18571
First edition
2014-08-01
Road vehicles — Objective rating
metric for non-ambiguous signals
Véhicules routiers — Mesures pour l’évaluation objective de signaux
non ambigus
Reference number
©
ISO 2014
© ISO 2014
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ii © ISO 2014 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms . 1
5 General data requirements . 4
6 ISO metric . 4
6.1 Calculation of the overall ISO rating . 5
6.2 Corridor score . 5
6.3 Phase, magnitude, and slope scores . 7
7 Meaning of the overall ISO rating .13
8 Pre-processing of the data .13
8.1 Synchronization of the signals .13
8.2 Sampling rate.14
8.3 Filtering .14
8.4 Interval of evaluation .14
9 Limitations .15
9.1 Type of signals .15
9.2 Metric validation .15
9.3 Meaning of the results .15
9.4 Multiple responses .15
Annex A (informative) Case studies .16
Bibliography .61
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
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on the ISO list of patent declarations received (see www.iso.org/patents).
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For an explanation on the meaning of ISO specific terms and expressions related to conformity
assessment, as well as information about ISO’s adherence to the WTO principles in the Technical Barriers
to Trade (TBT) see the following URL: Foreword - Supplementary information
The committee responsible for this document is ISO/TC 22, Road vehicles, Subcommittee SC 10, Impact
test procedures.
iv © ISO 2014 – All rights reserved

Introduction
Computer-aided engineering (CAE) has become a vital tool for product development in the automobile
industry. Various computer programs and models are developed to simulate dynamic systems. To
maximize the use of these models, the validity and predictive capabilities of these models need to be
assessed quantitatively. Model validation is the process of comparing CAE model outputs with test
measurements in order to assess the validity or predictive capabilities of the CAE model for its intended
usage. The fundamental concepts and terminology of model validation have been established mainly by
[1]
standard committees including the American Institute of Aeronautics and Astronautics (AIAA), the
American Society of Mechanical Engineers (ASME) Standards Committees on verification and validation
[2] [3]
of Computational Solid Mechanics and Computational Fluid Dynamics and Heat Transfer, the Defence
[4]
Modelling and Simulation Office (DMSO) of the United States Department of Defence (DoD), the United
[5] [19] [20]
States Department of Energy (DOE), and various other professional societies.
One of the critical tasks to achieve quantitative assessments of models is to develop a validation metric
that has the desirable metric properties to quantify the discrepancy between functional or time history
[6] [16] [17]
responses from both physical test and simulation result of a dynamic system.  Developing
quantitative model validation methods has attracted considerable researchers’ interest in recent
[11] [12] [13] [15] [17] [18] [23] [24] [25] [27]
years.     However, the primary consideration in the selection of an
effective metric should be based on the application requirements. In general, the validation metric is a
quantitative measurement of the degree of agreement between the physical test and simulation result.
[10]
This Technical Specification is the essential excerpt of ISO/TR 16250:2013 which provides
standardized calculations of the correlation between two signals of dynamic systems, and it is validated
against multiple vehicle safety case studies.
TECHNICAL SPECIFICATION ISO/TS 18571:2014(E)
Road vehicles — Objective rating metric for non-
ambiguous signals
1 Scope
This Technical Specification (TS) provides validation metrics and rating procedures to be used to
calculate the level of correlation between two non-ambiguous signals obtained from a physical test and
a computational model, and is aimed at vehicle safety applications. The objective comparison of time-
history signals of model and test is validated against various loading cases under different types of
physical loads such as forces, moments, and accelerations. However, other applications might be possible
too, but are not within the scope of this Technical Specification.
2 Normative references
There are no normative references used in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
filtering
smoothing of signals by using standardized algorithms
3.2
goodness or level of correlation
similarity of two signals
3.3
interval of evaluation
time domain that is used to calculate the correlation between two signals
3.4
rating
rating score
calculated value that represents a certain level of correlation (objective rating)
3.5
sampling rate
recording frequency of a signal
3.6
time sample
pair values (e.g. time and amplitude) of a recorded signal
3.7
time-history signal
physical value recorded in a time domain; those signals are non-ambiguous
4 Symbols and abbreviated terms
CAE Computer-aided engineering
CORA Correlation and analysis
DTW Dynamic time warping
EEARTH Enhanced error assessment of response time histories
SME Subject matter expert
a Relative half width of the inner corridor
b Relative half width of the outer corridor
C, C(t) Analysed signal (CAE signal)
ts ts
C , C (i) Truncated and shifted CAE curve
ts+d ts
C Derivative CAE curve, C
ts+w ts
C Warped CAE curve, C
DTW Dynamic time warping distance
DTW (i, j) Cost of the optimal warping path
opt
d Local cost matrix to perform the dynamic time warping
d(i, j) Local cost function to perform the dynamic time warping
dtw[i, j] Cumulative cost matrix
∆t Interval between two time samples
δ Half width of the inner corridor
i
δ (t) Lower/upper bounds of the inner corridor at time, t, (curve)
i
δ Half width of the outer corridor
o
δ (t) Lower/upper bounds of the outer corridor at time, t, (curve)
o
E Magnitude score
M
E Phase score
P
E Slope (topology) score
S
*
Maximum allowable magnitude error
ε
M
*
Maximum allowable percentage of time shift
ε
P
*
Maximum allowable slope error
ε
S
ε Magnitude error
mag
ε Slope error
slope
ts
i Index number of time shifted and truncated CAE curve, C
ts
i Index number of k-th warping path of curve, C
k
2 © ISO 2014 – All rights reserved

w ts
i Index number of warping path of CAE curve, C
ts
j Index number of time shifted and truncated test curve, T
ts
j Index number of k-th warping path of curve, T
k
w ts
j Index number of warping path of test curve, T
k Index number
k Exponent factor for calculating the magnitude score, E
M M
k Exponent factor for calculating the phase score, E
P P
k Exponent factor for calculating the slope score, E
S S
k Exponent factor for calculating the corridor score between the inner and outer
Z
corridors
m Time steps moved to evaluate the phase error
N Total number of sample points (e.g. time steps) between the starting time, t ,
start
and ending time, t
end
N All natural numbers without zero
> 0
ts ts
n Number of data samples of time shifted and truncated curves (C and T )
n Number of data samples of the optimal warping path
w
n Number of time shifts to get ρ
ε E
ρ Maximum cross correlation of all ρ (m) and ρ (m)
E L R
ρ (m) Cross correlation (signal is moved to the left)
L
ρ (m) Cross correlation (signal is moved to the right)
R
R Overall ISO rating
r Rank of the sliding scale of the ISO metric
SC (r) Lower threshold of rank, r
lower
SC (r) Upper threshold of rank, r
upper
T, T(t) Reference signal (test signal)
T Absolute maximum amplitude of the reference signal, T
norm
ts ts
T , T ( j) Truncated and shifted test curve
ts+d ts
T Derivative test curve, T
ts+w ts
T Warped test curve, T
t Time signal (axis of abscissa)
t Ending time of the interval of evaluation
end
t Starting time of the interval of evaluation
start
...