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How can I calculate a shock response spectrum (SRS) with Testlab ?

Experimenter
Experimenter

How do I calculate a Shock Response Spectrum (SRS) in Testlab?

 

Thanks for the help

4 REPLIES 4

Re: How can I calculate a shock response spectrum (SRS) with Testlab ?

Siemens Valued Contributor Siemens Valued Contributor
Siemens Valued Contributor

Quick and easy way is to use the Conditioning Toolbar, at top of the Navigator worksheet.

  • Drop your time signal into a display
  • Click on the curve in the display to 'select' it
  • Click the SRS Calculation button in the Conditioning toolbar
  • Fill in the desired parameters for the SRS calculation, click OK
  • The data in the display will be replaced with the Shock Response Spectrum.  The SRS will also be stored in a new folder (named Conditioning 1...) in your currently active project. 

SRS.png

 

Re: How can I calculate a shock response spectrum (SRS) with Testlab ?

Siemens Valued Contributor Siemens Valued Contributor
Siemens Valued Contributor

 

 

 

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.

 

SRS.gif

 

 

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

  • Start Desktop module ( Windows 10 : Start -> all programs-> SimCenter Testlab 18-> Desktop Standard & Advance)
  • Open project with time history data that will be used to create SRS
  • Create FrontBack picture then drag and drop time data file onto the picture to display time history data. The source of this can be either a time data block or from a Throughput file.

Q10_P3.png

 Q10_P4.png

 

 

 

  • Next select the curve in the FrontBack display by clicking on itQ10_P5.png

     

 

  • Then click on settings dialog icon located in conditioning toolbar at the top of the pageQ10_P6.png

     

 

  • Next click SRS icon located in conditioning toolbar at the top of the page to open parameters menu

 

Q10_P7.png

 

 

 

  • Using the SRS calculation parameter menu enter desired value

 

Q10_P8.png

 

 

 

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.

 

 

updated instance graphic.png

 

 

  • After entering parameters press the “OK” button
  • Note a folder in the current active section labeled “Conditioning 1” will be created with the results of the SRS calculation Q10_P10.png

     Q10_P11.png

     

 

 

Method 2 – Throughput Processing Worksheet

 

  • Start Desktop module ( Windows 10 : Start -> all programs-> SimCenter Testlab 18-> Desktop Standard & Advance)
  • Open ‘Signature Throughput Processing’ add-in (Tools -> Add-Ins -> Signature Throughput Processing-> ) check box on left side of screen then press closeQ10_P12.png

     

 

  • Check Time Data Selection Add-in as well
  • Load time history data into the input basket by right clicking on throughput data then select ‘Replace in Input Basket’
  • Next select the ‘Time Data Selection’ worksheet then press the ‘Replace’ button at top of the page to load the time data. 

Q10_P13.png

 

 

  • Next select the ‘Time Data Processing‘ worksheet
  • Select the time channel for processing by clicking check box on upper left corner of the page

Q10_P14.png

 

 

  • Next under Acquisition Parameters select ‘Change settings..’ then on ‘Tracking and Triggering’ tab set ‘measurement mode:’ to Stationary then ‘Method:’ to Free run and Number of average equal to ‘1’. Next under the FS Acquisition tab set the ‘Frame size’ parameter equal to the input time history recording length.Q10_P15.png

     

 

Q10_P16.png

  • Next under Channel Processing select ‘Change settings..’ then click on vibration tab and using ‘Function:’ drop down box to select Shock Response Spectrum Q10_P17.png

     

 

  • Next to enter the SRS calculation parameters press the ‘More…’ button. After entering the desired parameters close the ‘SRS calculation’ and ‘Channel Processing Settings’ windows.Q10_P18.png

     

 

  • The last step is to click on the ‘Calculate’ the buttonQ10_P19.png

     

 

  • Then to view the results return to the ‘ Navigator’ worksheetQ10_P20.png

     

 

 

 

 

 

Re: How can I calculate a shock response spectrum (SRS) with Testlab ?

Experimenter
Experimenter

Thanks for the quick response PMoore your suggestion worked great ! 

Re: How can I calculate a shock response spectrum (SRS) with Testlab ?

Experimenter
Experimenter

As well, thanks CharlesR for the details about the different SRS calculation parameters, it was very helpful...