01-07-2019 01:03 PM - edited 02-14-2019 04:22 PM
How do I calculate a Shock Response Spectrum (SRS) in Testlab?
Thanks for the help
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01-07-2019 01:34 PM - edited 02-15-2019 10:42 AM
Quick and easy way is to use the Conditioning Toolbar, at top of the Navigator worksheet.
01-07-2019 02:09 PM - edited 02-14-2019 04:27 PM
As PMoore demonstrated already Shock Response Spectrum calculations can be performed with the conditioning toolbar. Additionally, I wanted to mention that SRS calculations can be performed with throughput processing worksheet and give you some details about selecting the proper SRS parameters
Background
The Shock Response Spectrum (SRS) is a method to characterize events like earthquakes, shipboard shock from underwater explosions and spacecraft pyrotechnic shock. It applies an acceleration time history as a base excitation to an array of single-degree-of-freedom (SDOF) systems. The SRS values are the maximum absolute accelerations that the SDOF systems tuned to different natural frequencies would experience over the entire transient event. Since these values could actually represent a response in the positive, or negative direction also, this result is most
commonly used and is called the Maxi-Max response.
Note: The damping of each SDOF system is typically assumed as 5% (ξ), which is equivalent to Q = 10 ( amplification factor) Q=1/2ξ
Method 1 – Conditioning Toolbar
SRS Calculation Parameters -
Minimum & Maximum Frequency: Typically obtained from a MIL standard or based on expected range of natural frequencies of the Device under test (DUT). These values will be rounded to the nearest standard 1/n octave frequency.
Points per Octave: The number of points per octave is the number of SDOF systems per octave (or the number of resonant frequencies fn ) used in the derivation of the shock response spectrum.
Any arbitrary set of unique natural frequencies can be used for the shock response spectrum calculation. A typical scheme, however, is based on a proportional bandwidth, such as 1/6 octave. This means that the SDOF systems are designed to overlap and cover the complete frequency range of interest.
SRS Q Factor: Q=10 is the common Q factor assigned to the SDOF systems used to model the structure's behavior. The higher this Q factor, the higher the response oscillations and the higher the shock response spectrum values will be. The value used in the SRS calculation can be taken from a given specification or standard, or be based on known damping characteristics of the test structure which may have been determined experimentally.
Corrections: Pre-processing corrections can be performed to account for DC offset or drift related to measurement equipment and prevent leakage.
Instance: This specifies which part of the response period is used. The instance refers to the period of time of the input acceleration pulse during which the maximum response of the SDOF systems will be retained for the shock spectrum. It can take the values maximum, primary or residual. The primary time is the period during which the pulse is applied, while the residual time is that which follows, as shown in Figure below. In addition it is possible to select the options maximum absolute, positive or negative which means that the corresponding maximum overall value of response will be considered- which ever period it occurred in.
Amplitude: This determines which characteristic value of the response is to be used. The amplitude refers to the positive or negative response excursions of the SDOF system during which maxima are to be calculated and retained for the SRS. It can take the values absolute, positive or negative. Absolute takes the extreme value irrespective of the sign. All of these values are illustrated in Figure below.
Method 2 – Throughput Processing Worksheet
01-07-2019 03:29 PM - edited 02-14-2019 04:24 PM
Thanks for the quick response PMoore your suggestion worked great !
01-07-2019 03:32 PM - edited 02-14-2019 04:24 PM
As well, thanks CharlesR for the details about the different SRS calculation parameters, it was very helpful...