Robust: Road Upgrade of Standards GRD1-2002-70021. Acceleration - - PowerPoint PPT Presentation

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Robust: Road Upgrade of Standards GRD1-2002-70021. Acceleration transducers, data acquisition and validation. Marco Anghileri Dipartim ento di I ngegneria Aerospaziale Politecnico di Milano I taly Introduction Introduction The

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Marco Anghileri Dipartim ento di I ngegneria Aerospaziale Politecnico di Milano I taly

Robust: “Road Upgrade of Standards” GRD1-2002-70021. Acceleration transducers, data acquisition and validation.

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2 Bruxelles 30/05/2006

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Introduction Introduction

  • The comparison of severity indices and

time histories betw een test and simulation requires that the tool used to extract these information w orks in a proper w ay.

  • The definition and verification of

numerical data acquisitions and numerical transducers is then one the steps needed to assess the validation of the model.

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3 Bruxelles 30/05/2006

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Measure of severity indices and Measure of severity indices and time histories time histories

  • The numerical data acquisition must be

able to acquire data that can reconstruct properly the physics of the phenomenon.

  • The definition of the transducer must be

comparable to the behavior of a typical transducer used during crash tests.

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4 Bruxelles 30/05/2006

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Numerical data acquisition. Numerical data acquisition.

  • In order to collect the acceleration and

the velocity-time histories of the vehicle an accelerometer sensor is included in the vehicle model.

  • This element is represented by a rigid

brick that must be properly connected to a massive part of the vehicle, usually by means of a rigid link, in order to attenuate high frequencies components.

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5 Bruxelles 30/05/2006

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Location of the accelerometer Location of the accelerometer

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6 Bruxelles 30/05/2006

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Influence of sampling frequency Influence of sampling frequency

  • Round Robin scenario. Small vehicle 100 km/h 20° rigid

barrier.

  • Ls-dyna 970 solver up to 5434a version.
  • To verify the behavior of the numerical data acquisition

system, accelerations have been sampled at different frequencies.

  • Three output frequencies w ere considered:
  • 854 kHz (sampling time equal to the integration timestep),
  • 100 kHz
  • 10 kHz.
  • The data output file w ere used to compute the occupant

risk factors.

  • The output data w ere initially filtered w ith a standard

CFC180 filter and then processed by the softw are.

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7 Bruxelles 30/05/2006

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Comparison. Comparison.

  • The acceleration measures as the severity indices are

different even if they are referred to the same impact.

  • How can w e define w hich is the proper acceleration and

the w rong one and w hy an acceleration sampled during a numerical simulation can be w rong?

  • Besides the acceleration time history also the velocity

and displacement time histories can be obtained from these nodes.

  • To understand w hich is the right acceleration and

w hich is the w rong, w e must verify that:

– the velocity and the displacement obtained integrating the acceleration – And – the velocity and displacement directly sampled. – Must be equivalent

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8 Bruxelles 30/05/2006

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Lateral velocity comparison Lateral velocity comparison

  • 854 kHz
  • 100 Khz
  • 10 Khz

0 . 0 2 5 0 . 0 5 0 . 0 7 5 0 . 1 0 . 1 2 5 0 . 1 5

  • 8 0 0 0
  • 7 0 0 0
  • 6 0 0 0
  • 5 0 0 0
  • 4 0 0 0
  • 3 0 0 0
  • 2 0 0 0
  • 1 0 0 0

1 0 0 0 T i m e [ s ] Velocity [mm/s] V y 8 5 4 k H z S a m p l e d V y 8 5 4 k H z In t e g r a t e d

0 . 0 2 5 0 . 0 5 0 . 0 7 5 0 . 1 0 . 1 2 5 0 . 1 5

  • 8 0 0 0
  • 7 0 0 0
  • 6 0 0 0
  • 5 0 0 0
  • 4 0 0 0
  • 3 0 0 0
  • 2 0 0 0
  • 1 0 0 0

1 0 0 0 Velocity [mm/s] V y 1 0 0 k H z S a m p l e d V y 1 0 0 k H z I n t e g r a t e d 0 . 0 2 5 0 . 0 5 0 . 0 7 5 0 . 1 0 . 1 2 5 0 . 1 5

  • 1 4 0 0 0
  • 1 2 0 0 0
  • 1 0 0 0 0
  • 8 0 0 0
  • 6 0 0 0
  • 4 0 0 0
  • 2 0 0 0

2 0 0 0 T i m e [ s ] Velocity [mm/s] V y 1 0 k H z S a m p l e d V y 1 0 k H z I n t e g r a t e d

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9 Bruxelles 30/05/2006

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Vertical velocity comparison Vertical velocity comparison

  • 854 kHz
  • 100 Khz
  • 10 Khz

0 . 0 2 5 0 . 0 5 0 . 0 7 5 0 . 1 0 . 1 2 5 0 . 1 5

  • 1 0 0 0
  • 5 0 0

5 0 0 1 0 0 0 1 5 0 0 2 0 0 0 2 5 0 0 3 0 0 0 3 5 0 0 4 0 0 0 T i m e [ s ] Velocity [mm/s] V z 8 5 4 k H z S a m p l e d V z 8 5 4 k H z I n t e g r a t e d 0 . 0 2 5 0 . 0 5 0 . 0 7 5 0 . 1 0 . 1 2 5 0 . 1 5

  • 1 0 0 0
  • 5 0 0

5 0 0 1 0 0 0 1 5 0 0 2 0 0 0 2 5 0 0 3 0 0 0 3 5 0 0 4 0 0 0 T i m e [ s ] Velocity [mm/s] V z 1 0 0 k H z S a m p l e d V z 1 0 0 k H z I n t e g r a t e d 0 . 0 2 5 0 . 0 5 0 . 0 7 5 0 . 1 0 . 1 2 5 0 . 1 5

  • 2 0 0 0

2 0 0 0 4 0 0 0 6 0 0 0 8 0 0 0 1 0 0 0 0 T i m e [ s ] Velocity [mm/s] V z 1 0 k H z S a m p l e d V z 1 0 k H z I n t e g r a t e d

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10 Bruxelles 30/05/2006

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Comparison results. Comparison results.

  • Acceleration sampled at 854 Khz and 100Khz

are able to reconstruct correctly the velocity and the displacement of the vehicle.

  • Acceleration sampled at 10 Khz (standard

sampling rate used for experimental testing) is not able to reconstruct the motion of the vehicle.

  • Signals sampled at 10 Khz have aliasing

problems.

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11 Bruxelles 30/05/2006

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Data acquisition conclusion. Data acquisition conclusion.

  • This problem show ed 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.

  • This problem is mesh sensitive and code sensitive

(Pam crash has pre-sampling filtering).

  • The requirement is that, to prove the proper data

acquisition, the reconstruction of the motion must be demonstrated starting from acceleration time histories.

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12 Bruxelles 30/05/2006

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Numerical accelerometer definition. Numerical accelerometer definition.

  • Now that w e 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 w e w ant to compare these tw o output

these transducers (numerical and experimental) must be equivalent.

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Numerical-experimental Numerical-experimental transducers. transducers.

  • Numerical accelerometers are not damped. They

can produce frequencies up to the natural frequency of the element w here they are attached.

  • We have seen how to acquire these signals but

now w e must make them equivalent to the experimental ones

  • Typical real

accelerometer frequency response.

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Example applied to the Round Robin Example applied to the Round Robin Activity Activity

  • Round robin.
  • Experimental sampling rate :10 kHz
  • Numerical sampling rate: 100 kHz

0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 x 10

4

0.5 1 1.5 2 2.5 3 3.5 x 10

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frequency [hz] amplitude Spectrum Numerical original signal Numerical CFC1000 Numerical CFC600 NumericalCFC180 Numerical CFC60 Experimental unfiltered signal 0.5 1 1.5 2 2.5 x 10

4

2 4 6 8 10 12 14 16 x 10

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frequency [hz] amplitude Spectrum Numerical original signal Numerical CFC1000 Numerical CFC600 NumericalCFC180 Numerical CFC60 Experimental unfiltered signal 2000 4000 6000 8000 10000 12000 1 2 3 4 5 6 7 8 x 10

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frequency [hz] amplitude Spectrum Numerical original signal Numerical CFC1000 Numerical CFC600 NumericalCFC180 Numerical CFC60 Experimental unfiltered signal 1000 2000 3000 4000 5000 6000 0.5 1 1.5 2 2.5 3 3.5 4 x 10

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frequency [hz] amplitude Spectrum Numerical original signal Numerical CFC1000 Numerical CFC600 NumericalCFC180 Numerical CFC60 Experimental unfiltered signal 500 1000 1500 2000 2500 3000 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 x 10

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frequency [hz] amplitude Spectrum Numerical original signal Numerical CFC1000 Numerical CFC600 NumericalCFC180 Numerical CFC60 Experimental unfiltered signal 500 1000 1500 0.5 1 1.5 2 2.5 x 10

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frequency [hz] amplitude Spectrum Numerical CFC180 Numerical CFC60 Experimental unfiltered signal

Frequencies relevant for severety indices evaluation

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15 Bruxelles 30/05/2006

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Numerical signals. Conclusion. Numerical signals. Conclusion.

  • To correctly sample acceleration time

histories:

– Demonstrate that you are able to properly reconstruct the motion (w ith Geo Metro R4 100 kKhz).

  • To correctly compare the numerical

accelerometer to the experimental one:

– Pre-filter data to have a numerical frequency response similar to the experimental one (w ith Geo Metro R4 CFC60).