1、Best Practices Entry: Best Practice Info:a71 Committee Approval Date: 2000-07-24a71 Center Point of Contact: JPLa71 Submitted by: Wilson HarkinsSubject: Sinusoidal Vibration Practice: Subject assemblies and the full-up flight system to swept sinusoidal vibration.Abstract: Preferred Practice for Desi
2、gn & Test. Probability of failure is increased in flight due to low frequency transient environment. Some workmanship defects in large structures and full-up systems may go undetected. Subject assemblies and the full up flight system to swept sinusoidal vibration. This practice has been used on Mari
3、ner Series, Viking, Voyager, Galileo.Programs that Certify Usage: This practice has been used on Mariner Series, Viking, Voyager, Galileo.Center to Contact for Information: JPLImplementation Method: This Lesson Learned is based on Reliability Practice PT-TE-1406 from NASA Technical Memorandum 4322A,
4、 NASA Reliability Preferred Practices for Design and Test.Certain failures are not normally exposed by random vibration. Sinusoidal vibration permits greater displacement excitation of the test item in the lower frequencies.Provided by IHSNot for ResaleNo reproduction or networking permitted without
5、 license from IHS-,-,-Apply sinusoidal vibration to the test item by sweeping over a frequency range beginning at approximately 10 Hz ( one octave) up to approximately 100 Hz ( one octave). Sweep the frequency range at a logarithmic rate (i.e. delta f/f is constant). Sinusoidal vibration is performe
6、d with the same fixturing and concurrent with random vibration.Sinusoidal vibration is employed to simulate the effects of significant flight environment launch transients. These transients typically produce the dominant loading on primary and secondary structure and many of the larger subsystems an
7、d assemblies. Sinusoidal vibration is the only widespread current method of adequately exciting the lower frequency dynamic modes - particularly those below approximately 40 Hz. Sweeping at a log rate between 1 octave/minute and 6 octaves/minute should avoid application of excessive fatigue cycles.
8、The higher rate is near the upper limit which most control systems can accommodate without experiencing some instability. The use of logarithmic sweep rates has the advantage in that a nearly equal time is spent at resonance for a given Q, independent of frequency.Sinusoidal vibration levels can be
9、derived as in the following example:Step 1. Create analytically derived transient waveforms from various flight events: refer to D descriptionD Step 2. Compute the shock spectra for each of the waveforms in Step 1:Provided by IHSNot for ResaleNo reproduction or networking permitted without license f
10、rom IHS-,-,-refer to D descriptionD Step 3. Take data from previous flight measurements:refer to D descriptionD Step 4. Combine results from steps 2, and 3 and envelope:Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-refer to D descriptionD Step 5. C
11、onvert to a sine amplitude equivalent vs. frequency by dividing Shock Response Spectrum envelope in Step 4 by Q:Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-refer to D descriptionD Alternatives to the use of swept sine vibration testing are curren
12、tly under development which address several of the objections to this method. In particular, the problem of excessive resonance build-up in a sinusoidal vibration sweep relative to the flight transient environment may be alleviated by any of the following tests:a71 Narrow band swept random.a71 Discr
13、ete frequency sinusoidal pulses applied at regular frequency intervals.a71 Complex waveform pulses representative of a composite of the various launch transient events.Impact of Non-Practice: Probability of failure is increased in flight due to low frequency transient environment. Some workmanship d
14、efects in large structures and full-up systems may go undetected.Related Practices: N/AProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Additional Info: Approval Info: a71 Approval Date: 2000-07-24a71 Approval Name: Eric Raynora71 Approval Organization: QSa71 Approval Phone Number: 202-358-4738Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
