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

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 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 Robust. GRD1-2002-70021 proper w ay. • The definition and verification of 2 numerical data acquisitions and numerical transducers is then one the steps needed to assess the validation of the model. 2 Bruxelles 30/05/2006

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. Robust. GRD1-2002-70021 • The definition of the transducer must be comparable to the behavior of a typical 3 transducer used during crash tests. 3 Bruxelles 30/05/2006

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. Robust. GRD1-2002-70021 • This element is represented by a rigid brick that must be properly connected 4 to a massive part of the vehicle, usually by means of a rigid link, in order to attenuate high frequencies components. 4 Bruxelles 30/05/2006

Location of the accelerometer Location of the accelerometer Bruxelles 30/05/2006 5 Robust. GRD1-2002-70021 5

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. Robust. GRD1-2002-70021 • Three output frequencies w ere considered: • 854 kHz (sampling time equal to the integration timestep), • 100 kHz 6 • 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. 6 Bruxelles 30/05/2006

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 Robust. GRD1-2002-70021 and displacement time histories can be obtained from these nodes. • To understand w hich is the right acceleration and 7 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 7 Bruxelles 30/05/2006

Lateral velocity comparison Lateral velocity comparison 1 0 0 0 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 • 854 kHz - 1 0 0 0 - 2 0 0 0 Velocity [mm/s] - 3 0 0 0 - 4 0 0 0 - 5 0 0 0 - 6 0 0 0 - 7 0 0 0 - 8 0 0 0 0 0 . 0 2 5 0 . 0 5 0 . 0 7 5 0 . 1 0 . 1 2 5 0 . 1 5 T i m e [ s ] Robust. GRD1-2002-70021 1 0 0 0 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 • 100 Khz - 1 0 0 0 - 2 0 0 0 Velocity [mm/s] - 3 0 0 0 - 4 0 0 0 8 - 5 0 0 0 - 6 0 0 0 - 7 0 0 0 - 8 0 0 0 0 0 . 0 2 5 0 . 0 5 0 . 0 7 5 0 . 1 0 . 1 2 5 0 . 1 5 2 0 0 0 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 0 • 10 Khz - 2 0 0 0 - 4 0 0 0 Velocity [mm/s] - 6 0 0 0 - 8 0 0 0 - 1 0 0 0 0 - 1 2 0 0 0 8 Bruxelles 30/05/2006 - 1 4 0 0 0 0 0 . 0 2 5 0 . 0 5 0 . 0 7 5 0 . 1 0 . 1 2 5 0 . 1 5 T i m e [ s ]

Vertical velocity comparison Vertical velocity comparison 4 0 0 0 V z 8 5 4 k H z S a m p l e d 3 5 0 0 V z 8 5 4 k H z I n t e g r a t e d 3 0 0 0 • 854 kHz 2 5 0 0 Velocity [mm/s] 2 0 0 0 1 5 0 0 1 0 0 0 5 0 0 0 - 5 0 0 - 1 0 0 0 0 0 . 0 2 5 0 . 0 5 0 . 0 7 5 0 . 1 0 . 1 2 5 0 . 1 5 T i m e [ s ] 4 0 0 0 V z 1 0 0 k H z S a m p l e d 3 5 0 0 V z 1 0 0 k H z I n t e g r a t e d Robust. GRD1-2002-70021 3 0 0 0 2 5 0 0 • 100 Khz Velocity [mm/s] 2 0 0 0 1 5 0 0 1 0 0 0 5 0 0 9 0 - 5 0 0 - 1 0 0 0 0 0 . 0 2 5 0 . 0 5 0 . 0 7 5 0 . 1 0 . 1 2 5 0 . 1 5 T i m e [ s ] 1 0 0 0 0 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 8 0 0 0 6 0 0 0 • 10 Khz Velocity [mm/s] 4 0 0 0 2 0 0 0 0 9 Bruxelles 30/05/2006 - 2 0 0 0 0 0 . 0 2 5 0 . 0 5 0 . 0 7 5 0 . 1 0 . 1 2 5 0 . 1 5 T i m e [ s ]

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 Robust. GRD1-2002-70021 not able to reconstruct the motion of the vehicle. 10 • Signals sampled at 10 Khz have aliasing problems. 10 Bruxelles 30/05/2006

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. Robust. GRD1-2002-70021 • This problem is mesh sensitive and code sensitive (Pam crash has pre-sampling filtering). 11 • The requirement is that, to prove the proper data acquisition, the reconstruction of the motion must be demonstrated starting from acceleration time histories. 11 Bruxelles 30/05/2006

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. Robust. GRD1-2002-70021 • This numerical transducer must be compared to a standard real transducer. 12 • If w e w ant to compare these tw o output these transducers (numerical and experimental) must be equivalent. 12 Bruxelles 30/05/2006

Numerical-experimental Numerical-experimental transducers. transducers. • Typical real accelerometer frequency response. Robust. GRD1-2002-70021 • Numerical accelerometers are not damped. They 13 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 13 Bruxelles 30/05/2006

Example applied to the Round Robin Example applied to the Round Robin Activity Activity Frequencies relevant for 13 Spectrum x 10 12 3.5 Spectrum x 10 severety indices evaluation 12 Spectrum Numerical original signal x 10 12 Numerical CFC1000 Spectrum Numerical original signal x 10 11 12 Spectrum Spectrum Numerical CFC600 Numerical CFC1000 x 10 x 10 Numerical original signal • Round robin. 16 NumericalCFC180 Numerical CFC600 Numerical CFC1000 Numerical original signal 3 8 Numerical original signal Numerical CFC180 Numerical CFC60 NumericalCFC180 Numerical CFC600 Numerical CFC1000 4 Numerical CFC60 Numerical CFC1000 Experimental unfiltered signal Numerical CFC60 NumericalCFC180 Numerical CFC600 2 • Experimental sampling rate :10 kHz Experimental unfiltered signal Numerical CFC600 Experimental unfiltered signal Numerical CFC60 NumericalCFC180 14 2.5 NumericalCFC180 Experimental unfiltered signal Numerical CFC60 7 Numerical CFC60 2.5 Experimental unfiltered signal 3.5 1.8 Experimental unfiltered signal • Numerical sampling rate: 100 kHz 12 6 1.6 2 3 2 amplitude Robust. GRD1-2002-70021 10 amplitude 1.4 5 amplitude 2.5 amplitude 1.5 amplitude amplitude 8 1.2 1.5 4 2 14 1 6 1 3 1.5 0.8 1 4 2 0.6 0.5 1 2 0.4 0.5 1 0.5 0 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 0.2 0 0 0.5 1 1.5 2 2.5 frequency [hz] 4 0 x 10 0 2000 4000 6000 8000 10000 12000 frequency [hz] 4 0 x 10 0 0 0 1000 2000 3000 4000 5000 6000 frequency [hz] 0 0 500 1000 500 1500 1000 2000 2500 1500 3000 frequency [hz] 14 Bruxelles 30/05/2006 frequency [hz] frequency [hz]

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 Robust. GRD1-2002-70021 100 kKhz). • To correctly compare the numerical accelerometer to the experimental one: 15 – Pre-filter data to have a numerical frequency response similar to the experimental one (w ith Geo Metro R4 CFC60). 15 Bruxelles 30/05/2006