Session: 28 - 06: Experimental Techniques and Validation in Turbomachinery

Submission Number: 179191

Synthesizing Time Domain Signal From SRS Using Different Methods and Their Equivalent Response Validation 

An aircraft typically includes and auxiliary power unit (APU) for main engine starting and electrical power to the aircraft during both ground and flight operation.  Due to the APU characteristics, high speed, rotor and exhaust noise, these are installed in the aircraft in remote locations which present challenging shock and vibration environmental conditions for the APU.  There are four types of shock environmental in Mil-std-810[1]: (1) “TWR” (Time Waveform Replication) [1], implies that the measured time history will be reproduced on the laboratory environment with the minimal amplitude time history error.   Typically implemented using special shock package software for replication.  (2) “Classical pulse” [1] (terminal peak sawtooth, trapezoidal and half-sine pulses), This category is generally employed when suitable field measurement information is unavailable, and traditional testing is relied upon.  (3) “ Shock Response spectrum (SRS)” refers to cases in which an SRS is used for the test specification, and exciter shock is synthesized. (4) pyro shock (Pyro shock tests involving pyrotechnic (explosive- or propellant-activated), which is like SRS. 

In general, SRS type shock is considered in the paper to synthesize the time history.   There are two methods in literature, which are as follows:

1. Damped sinusoids

2. Wavelets based formulation. 

  SRS approached is challenging due to lack of phase information (if measured data are not available), hence become iterative in nature to create the time history.

In this paper, the following contribution can be provided:

1.      A sample SRS is selected using MIL standard or similar.

2.      Convert time history using the above-mentioned two methods.  During this synthesize, sampling rate, octave bands, and different strategy to form time history are studied.

3.      For design, response SRS predicted based on the natural frequency and damping of the system.

4.       Validated with test result for the item # 3.

 

References

MIL-STD-810H, “ENVIRONMENTAL ENGINEERING CONSIDERATIONS AND LABORATORY TESTS”,  DEPARTMENT OF DEFENSE TEST METHOD STANDARD, 2019.

Ferebee, R. C.,  Clayton, J.,  Alldredge, D., and Irvine, T., “An alternative method  of specifying Shock test criteria”,   NASA/TM-2008-215253. 

S. Allen, “Waveform Synthesis for Shock Response Spectrum Replication, Applied To Ground Vehicle Component Testing”, In Proceedings of the Ground Vehicle Systems Engineering and Technology Symposium (GVSETS), NDIA, Novi, MI, Aug. 13-15, 2019.

C. Lalanne, Sinusoidal Vibration (Mechanical Vibration and Shock), New York: Taylor & Francis, 1999.

A. Piersol and T. Paez, Harris’ Shock and Vibration Handbook, 6th Edition; V. Bateman, Shock Testing Machines, Chapter 27, New York City: McGraw-Hill, 2010.

H. Gaberson, "Shock Severity Estimation," Sound & Vibration, January 2012.

W. Kacena, M. McGrath and A. Rader, "Aerospace Systems Pyrotechnic Shock Data, Vol. VI., NASA CR 116406," Goddard Space Flight Center, Maryland, 1970.

European Cooperation for Space Standardization, "Mechanical Shock Design and Verification Handbook," Noordwijk, The Netherlands, July 2015.

Himelblau et al, NASA-HDBK-7005, Dynamic Environmental Criteria, Washington DC: National Aeronautics and Space Administration, 2001.

Presenting Author: Parag Mathuria Pratt & Whitney

Presenting Author Biography: Currently working at Pratt & Whitney at rotor dynamics.

Authors:

Parag Mathuria Pratt & Whitney
James Taubler Pratt & Whitney
Gregory Savela Pratt & Whitney