*This post is a work-in-progress… *

Combined Ascent Loads for Launch Vehicle Analysis

Equivalent Axial & Line Loads for Launch Vehicles

– Tom Irvine

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*This post is a work-in-progress… *

Combined Ascent Loads for Launch Vehicle Analysis

Equivalent Axial & Line Loads for Launch Vehicles

– Tom Irvine

*This is a work-in-progress…
*

I am creating a series of webinars with Matlab exercises for fatigue analysis

Matlab script: Vibrationdata Signal Analysis Package

Here are the slides:

Unit 5 Rainflow Cycle Counting, Time Domain

Unit 7 Synthesizing a Time History to Satisfy a PSD Specification

Unit 8 Drop & Classical Shock & Video Half-Sine SRS Animation

Unit 9 Seismic & Pyrotechnic Shock & Video Delta 4 Shock Events

Unit 11 Vibration Response Spectrum

Unit 12 Rainflow Fatigue, Spectral Methods, Fatigue Damage Spectrum

Unit 13 Modifying Spectral Fatigue Methods for S-N Curves with MIL-HDBK-5J Coefficients

Unit 14a Enveloping Nonstationary Vibration via Fatigue Damage Spectra

Unit 14b Enveloping Nonstationary Vibration, Batch Mode for Multiple Inputs

Unit 15 Using Fatigue to Compare Sine and Random Environments

Unit 16 Sine-on-random Conversion to a PSD via Fatigue Damage Spectra

Unit 17 Non-Gaussian Random Fatigue and Peak Response

Unit 20 Fatigue Damage including Mean Stress

Unit 21 Electronic Circuit Board Fatigue, Part 1

Unit 22 Electronic Circuit Board Fatigue, Part 2

Unit 23 Time-Level Equivalence

Unit 24 Multiaxis Fatigue, Constant Amplitude Loading

Unit 25 Multiaxis Fatigue, Stress Ratio Methods

Unit 26 Multiaxis Fatigue, Variable Amplitude Loading

Unit 27 Airbus Fatigue Manual

*More later…
*

– Tom Irvine

The top figure is the time history from the El Centro earthquake, North-South horizontal component. The middle is the corresponding Waterfall SRS with 4 second segments and with 50% overlap. The bottom is the spectrogram.

The Waterfall SRS is calculated by first taking the complete response time history for each natural frequency of interest. Then the time history for each is divided into segments. Finally, the shock response spectrum (SRS) is taken for each natural frequency and for each segment, by taking the peak positive and peak negative responses.

The Waterfall SRS function is given in:

Matlab script: Vibrationdata Signal Analysis Package

>> vibrationdata > Time History > Shock Response Spectrum, Various > Waterfall SRS

See also: El Centro Earthquake

– Tom Irvine

*Another work-in-progress…*

Step 1: Download a video file.

Step 2: Play using VLC media player.

* * * * *

Launch Vehicles

Delta 4 Heavy Launch Vehicle Shock Events

* * * * *

Helicopters

* * * * *

Fixed Wing Aircraft

* * * * *

Automotive & Transportation

* * * * *

Shock & Vibration Testing

* * * * *

Fluid Systems

* * * * *

Miscellaneous

Equipment must be designed and tested to withstand shock and vibration. Ideally, all equipment would be tested on a shaker table with six-degree-of-freedom control (three translations and three rotations). Such tables and control systems exist but are very expensive. Furthermore, any multi-axis testing requires careful consideration of phase angles between the six degrees.

Another option is to test equipment on a triaxial table where the three translations are controlled, and the three rotational degrees are constrained to zero motion. Testing on a biaxial table is yet another choice.

The most common test method, however, remains testing in each of three orthogonal axes, one axis at a time, on a single-axis shaker. This is simplest and least expensive method.

The question arises “Should the acceleration level be increased for the case of single-axis testing?”

There is a tacit understanding that aerospace and military equipment test levels already have a sufficient uncertainty margin or safety factor so that the levels can be used without further increase. In other words, the specifications are already intended for single-axis testing. In many cases, a uniform level is used in each axis which is the maximum envelope of the maximum expected levels in the three axes plus some margin.

* * *

The standards which address testing equipment for earthquakes take a different approach. The following descriptions are taken from five common standards.

Only KTA 2201.4 gives a scaling formula. This is also the only standard from the five samples which may be freely downloaded.

* * *

IEEE 344-2013 Standard for Seismic Qualification of Equipment for Nuclear Power Generating Stations

8.6.6 Multiaxis tests

Seismic ground motion occurs simultaneously in all directions in a random fashion. However, for test purposes, single-axis, biaxial, and triaxial tests are allowed. If single-axis or biaxial tests are used to simulate the 3D environment, they should be applied in a conservative manner to account for the absence of input motion in the other orthogonal direction(s). One factor to be considered is the 3D characteristics of the input motion. Other factors are the dynamic characteristics of the equipment, flexible or rigid, and the

degree of spatial cross-coupling response. Single and biaxial tests should be applied to produce adequate levels of excitation to equipment where cross coupling is significant and yet minimize the level of overtesting where the cross coupling is not significant.

* * *

KTA 2201.4 Design of Nuclear Power Plants against Seismic Events, Part 4: Components

This document may be freely downloaded: link

See paragraphs

5.3.3 Excitation Axes

5.5.2.5 Simultaneity of excitation directions

Simultaneous three-axis testing is preferred. But single-axis testing can be substituted by testing in each of three axes sequentially.

The standard shows, for example, that the uniform single-axis level should be the “square root of the sum of the squares” of the three orthogonal installation site levels.

* * *

IEC 980 Recommended practices for seismic qualification of electrical equipment of the safety system for nuclear generating stations

6.2.9 Qualification test method

6.2.9.1 General

As is well known, seismic excitation occurs simultaneously in all directions in a random way. According to this point of view, the test input motion should consist of three mutually independent waveforms applied simultaneously along the three orthogonal axes of the equipment.

However, taking into account that three axial testing installations are rare and that triaxial testing is desirable when significant coupling exists simultaneously between the two preferred horizontal axis of the specimens, biaxial testing with multifrequency independent input motion in the horizontal and vertical direction is an acceptable test.

Tests shall be performed according to 6.3.2 and, in terms of total duration and fatigue induced, are intended to become conservative.

In some cases, single axis tests with multiple, or single frequency excitation are also acceptable methods of test if properly justified considering the effect of coupling between axes.

* * *

Telcordia GR-63-CORE

Assumes single-axis testing. The base input time history is specified in the standard.

* * *

IEEE 693-2005 – IEEE Recommended Practice for Seismic Design of Substations

paragraph 4.9

The shaker table shall be biaxial with triaxial preferred.

* * *

See also:

Seismic Test & Analysis Webinars

– Tom Irvine

Here is a listing of the webinars and related materials.

Matlab script: Vibrationdata Signal Analysis Package

6. Leakage Error, Hanning Window

7. FFTs

12. Power Spectral Density Functions of Measured Data

13. SDOF Response to Power Spectral Density Base Input

14. Synthesizing a Time History to Satisfy a PSD Specification

15. SDOF Response to Base Input in the Frequency Domain

16. Vibration Response Spectrum

17. SDOF Response to Applied Force

18. Force Vibration Response Spectrum

21. Integration & Differentiation of Time Histories

22. Integration and Differentiation of Time Histories & Spectral Functions

24. Seismic Shock

27. SRS Synthesis

28. Multi-degree-of-freedom SRS

29. Stress-Velocity Relationship

30. Rectangular Plate Shock & Vibration

31. Rectangular & Circular Plate Shock & Vibration

32. Electronic Circuit Board Fatigue

33. Rainflow Fatigue

34. Rainflow Fatigue for Continuous Beams

35. Using Fatigue to Compare Sine and Random Environments

36. Non-Gaussian Random Fatigue and Peak Response

37. Acoustic Fatigue

38. Electronic Circuit Board Fatigue Part 2

40. Shock Fatigue

43. Two-degree-of-freedom System, Two-stage Isolation

44. Sine Filtering

45. Two-degree-of-freedom System with Rotation and Translation

46. Two-degree-of-freedom System with Multi-point Enforced Motion

47. Shock Response Spectrum Synthesis, Special Topics

Seismic Test & Analysis Webinars

Circuit Board Shock & Vibration Analysis

HALT/HASS for Product Reliability

*More later. . .*

– Tom Irvine

*This is a work-in-progress…
*

I am creating a series of webinars with Matlab exercises for seismic testing.

Here are the slides.

Telcordia Technologies Generic Requirements GR-63-CORE: Bellcore_GR_63_Core.ppt

*This unit contains an alternative waveform for VERTEQII.*

CEI.IEC 980, Recommended practices for seismic qualification of electrical equipment of the safety system for nuclear generating stations: CEI/IEC 980: 1989

IEEE Std 693-2005, Recommended Practice for Seismic Design of Substations: IEEE_693_sine_beat.pptx

IEEE Standard for Seismic Qualification of Equipment for Nuclear Power Generating

Stations: IEEE_std_344.ppt

Matlab script: Vibrationdata Signal Analysis Package

* * *

See also:

Cummins Generator Seismic Shaker Test

Webinar 47 – Shock Response Spectrum Synthesis, Special Topics

Seismic Peak Ground Acceleration

Some Earthquake Engineering Terminology

* * *

– Tom Irvine

*You are welcome to participate in any of the following courses.*

I will teach shock & vibration course in Trieste, Italy on January 25-27, 2017. Course Link

* * *

I will teach a shock & vibration finite element analysis course in Singapore, February 13-15, 2017. Brochure Link

Thank you,

Tom Irvine

*This is a work-in-progress…
*

I am creating a series of webinars with Matlab exercises for structural dynamics and finite element analysis.

Here are the slides:

Unit 6 Applied Force Response Analysis

Unit 7 Response to Seismic Base Mass Excitation

Unit 8 Response to Enforced Motion

Unit 10 Beam Bending FEA with Added Mass and Stiffness

Unit 11 Beam Bending FEA with Steady-State Sinusoidal Base Excitation

Unit 12 Beam Bending FEA with Sine Sweep Base Excitation

Unit 13 Beam Bending FEA with PSD Base Excitation

Unit 14 Beam Bending FEA Fatigue

Unit 15 Beam Bending FEA Shock

Unit 17 FEA: Circuit Board Natural Frequencies

Unit 18 FEA: Circuit Board Damping

Unit 19 FEA: Circuit Board Response to Sine Vibration

Unit 20 FEA: Circuit Board Response to Sine Sweep Vibration

Unit 21 FEA: Circuit Board Response to Random Vibration

Unit 22 FEA: Circuit Board Response to PSD Synthesis

Unit 23_FEA: Circuit Board Shock Response Spectra & Synthesis

Unit 24_FEA: Circuit Board MDOF Shock

Unit 25: FEA: Circuit Board Fatigue

Special Topic: Irvine_multiaxis_fatigue.pptx

Matlab script: Vibrationdata Signal Analysis Package

* * *

See also:

Transfer Functions from Normal Modes

Convert Modal Damping to a Damping Coefficient Matrix

Beam Bending, Finite Element Analysis

The Mode Acceleration Method MA_method.pdf

The Modal Truncation Augmentation Method: MTAM.pdf

*This is also known as the residual vector method. *

* * *

– Tom Irvine

Figure 1. A320 Takeoff

I recently flew as a passenger in an A320 similar to the aircraft shown in Figure 1.

Figure 2. Time History Plots

The takeoff vibration is shown in Figure 2 for the lateral and vertical axes. The aircraft went airborne at 393 seconds. The fore-aft axis is omitted since its level was lower. The sensor was a Slam Stick X mounted on the cabin floor.

Figure 3. PSD, Lateral Axis

Figure 4. PSD, Vertical Axis

The PSD plots show some distinct spectral peaks which are most likely forcing frequencies, or possibly lightly-damped structural resonances.

Here is the time history data file: takeoff_data

– Tom Irvine

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