April 2014 

NASA/CR–2014-218248 

Calibration of International Space Station (ISS) 

Node 1 Vibro-Acoustic Model 

Weiguo Zhang and Ravi Raveendra 

Comet Technology Corporation, Ann Arbor, Michigan 
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April 2014 

NASA/CR–2014-218248 

Calibration of International Space Station (ISS) 

Node 1 Vibro-Acoustic Model 

Weiguo Zhang and Ravi Raveendra 

Comet Technology Corporation, Ann Arbor, Michigan 
Available from: 

NASA Center for AeroSpace Information 

7115 Standard Drive 

Hanover, MD 21076-1320 

443-757-5802 
- 1 -

1. 0 Introduction 

The objective of the present investigation is to correlate the vibration data measured by 

NASA using acoustic emission, at specific sensor locations on Node 1 of the 

International Space Station (ISS), to corresponding values predicted by Comet EnFlow, 

an analysis software based on Energy Finite Element Method (EFEM) that was 

developed previously as a result of an SBIR funding from NASA LaRC. The report is 

arranged as follows: Section 2 provides a brief description of measured data, Section 3 

describes the computational model, Section 4 describes the results and brief remarks are 

provided in the final section. 

2.0 Measured Data 

The measured data was provided by NASA and a brief description of the data is provided 

in this section. The Node 1 Model is shown in Figure 1. The vibrations are measured 

using a series of acoustic emission sensors that have been placed at the locations as 

shown in Figure 2; Sensor 13 is the source location that corresponds to input excitation at 

the wall. The coordinates of the sensor location are presented in Table 1. 

 

Figure1. Node 1 Structure 
- 2 -

Figure 2. Sensor Locations 

Table 1. Coordinates of Sensor Locations 

The B225.5 acoustic emission sensors are utilized for measurement. The averaged power 

spectra density of the sensor voltage at measurement locations is provided in Figure 3. 

Note that the data at location 2 is not included since the corresponding receiver channel was 

not working properly. The most signal energy is between 40 kHz and 160 kHz. The 

calibration results at these frequencies are plotted in Figure 4. The curve indicates the flat 

response from 60 kHz to 180 kHz with 57 dB (708 V/ȝm) calibration factor. The flexural 

velocity at these measurement locations are computed from data from Figure 3 and 

Figure 4 which are reported in Section 4.0. 

R= 80.25 barrel section

ID R=80.25 

Starboard hatch 

centerline = 0o cone section

Detectors

Axial distance (in) 

from aft end Radial (degrees)

Radial distance (in) 

from cone outer edge

Radial 

(degrees)

Radial distance (in) 

from "cone apex" 

1 73 135.71

2 5.5 144.15

3 Aft cone 43.24 280.5 46.47

4 14.75 322.19

5 81.00 315.85

6 94.25 224.15

7 Forward cone 42.74 262.2 46.97

13 Forward cone 20 181 69.71

Source Forward cone 20 180 69.71
- 3 -

Spectral Transfer Function--Hole 0.173 (set 1-1)

0.000001

0.00001

0.0001

0.001

0.01

0.1

1

0 100 200 300 400 500

Frequency (kHz)

Voltage

Location 1

Location 3

Location 13

Location 4

Location 5

Location 6

Location 7

Background

Figure 3. Power Spectra Density of Measurement Data 

Figure 4. Conversion Factor from Voltage to Displacement 

10

20

30

40

50

60

70

0 50 100 150 200

B225-5 Calibration

(20 kHz high pass filtering)

225 Cal - NIST on plate

225 Cal - IF on steel block

Flat bandwidth region

dB (ref 1 V/μm)

Frequency (kHz)
- 4 -

3.0 EFEM Modeling of Node 1 of the Space Station 

Figure 5. The FEM model of Node 1 for Stress Analysis 

A very dense finite element (high fidelity) model of Node 1 (see Figure 5) that was 

originally created for stress analysis was provided by Boeing. The model also included 

material and geometry properties except damping coefficients. This model consisted of 

61167 elements and 54517 nodes. Comet EnFlow is based on finite element method for 

high frequency vibroacoustic analysis. In this method, energy density is used as the 

primary variable. Since the energy density does not vary spatially very much, the mesh 

density requirements are much less and as a result a low density (intermediate fidelity) 

finite element model is appropriate. Thus, the original FEM model is coarsened and 

simplified for EnFlow analysis. Specially, the small parts, such as, clips, small overlap 

plates etc., are replaced by equivalent plates. In addition, the multiple attachments on the 

four hatch area and aft and forward end cone have less effect on the wave propagation on 

the wall of the Node 1. These elements are neglected and the effects are considered via 

modifying the properties of the supporting plates. Finally, the rigid bar elements are 

neglected since no vibration energy is transported through them. 

The modified finite element model for EnFlow analysis is shown in Figure 6. EFEM 

requires the generation of joint element at geometric and material discontinuities. The 

joint elements (see Figure 7) are automatically created the graphical user interface utility 

of Comet EnFlow. The new model including the joint element is comprised of 11126 

elements, 15851 nodes and 3342 joint elements. Note that solutions in vibroacoustic 

analysis are required at many frequencies. As a result of the reduction of the model, the 

solution times become reasonable. 
- 5 -

Figure 6. The FEM model of Node 1 for EnFlow Analysis 

Figure 7. The Joint Location in Node 1 EnFlow Model 
- 6 -

4.0 Correlation of Experimental Data to EFEM Predictions 

Comet/EnFlow is used to predict the noise distribution due to the wave propagation 

from the source location (sensor 13). In this study, the noise corresponds to flexural 

velocity on the wall of Nodal 1. 

The flexural velocity at sensor 13 which is close the source location is converted to 

flexural acceleration and utilized as the excitation on the corresponding node of the 

EnFlow model. The flexural velocity at center frequency of 1/3 octave band from 40 

kHz to 160 kHz is computed. The damping coefficient is linearly distributed over the 

whole frequency range which is shown in Figure 8. 

0

0.0005

0.001

0.0015

0.002

0.0025

40 60 80 100 120 140 160

Frequency (kHz)

Damping Coeff.

Figure 8. Damping coefficient over the frequency range 

The flexural velocity distribution at 40 kHz is shown in Figure 9. It can be observed 

that the magnitude of the velocity decreases along the distance to the source location. 

The flexural energy intensity plot over the model in Figure 10 displays how flexural 

energy propagates on the wall of the model. 
- 7 -

Figure 9. The Flexural Velocity Distribution at 40 kHz 

Figure 10. The Flexural Energy Intensity Vector Plot at 40 kHz 
- 8 -

The flexural velocities computed by Comet EnFlow at the sensor locations are shown 

from Figure 11~ Figure 17. These figures are arranged in the sequence of distance 

from the sensors to the source. The measured flexural velocity at the center 

frequencies is obtained via averaging over the 1/3 octave band and also plotted in the 

corresponding Figures. 

0.00001

0.0001

0.001

0.01

0.1

1

40 70 100 130 160

Frequency (kHz)

Velocity (in/sec)

Measured

Measured(Averaged)

EnFlow

Figure 11. Flexural Velocity of Sensor 13 
 - 9 -

0.0000001

0.000001

0.00001

0.0001

0.001

0.01

0.1

1

40 70 100 130 160

Frequency (kHz)

Velocity (in/sec)

Measured

Measured(Averaged)

EnFlow

 Figure 12. Flexural Velocity of Sensor 7 

0.0000001

0.000001

0.00001

0.0001

0.001

0.01

0.1

1

40 70 100 130 160

Frequency (kHz)

Velocity (in/sec)

Measured

Measured(Averaged)

EnFlow

Figure 13. Flexural Velocity of Sensor 6 
 - 10 -

0.0000001

0.000001

0.00001

0.0001

0.001

0.01

0.1

1

40 70 100 130 160

Frequency (kHz)

Velocity (in/sec)

Measured

Measured(Averaged)

EnFlow

Figure 14. Flexural Velocity of Sensor 1 

0.0000001

0.000001

0.00001

0.0001

0.001

0.01

0.1

1

40 70 100 130 160

Frequency (kHz)

Velocity (in/sec)

Measured

Measured(Averaged)

EnFlow

Figure 15. Flexural Velocity of Sensor 5 
 - 11 -

0.0000001

0.000001

0.00001

0.0001

0.001

0.01

0.1

1

40 70 100 130 160

Frequency (kHz)

Velocity (in/sec)

Measured

Measured(Averaged)

EnFlow

Figure 16. Flexural Velocity of Sensor 4 

0.0000001

0.000001

0.00001

0.0001

0.001

0.01

0.1

1

40 70 100 130 160

Frequency (kHz)

Velocity (in/sec)

Measured

Measured(Averaged)

EnFlow

Figure 17. Flexural Velocity of Sensor 3 
 - 12 -

5.0 Remarks 

Overall, good correlations are obtained. The flexural velocity by EnFlow at sensor 13 

is identical to the measured data which indicates that the proper acceleration 

excitation is applied on the EnFlow model. The flexural velocity by EnFlow at sensor 

7, sensor 6, sensor 1 and sensor 5 correlates well with the measured data. The Note 

that these four sensors are relatively close to the source location. The results 

demonstrate that the EnFlow captures properly the energy decay away from the 

source. Nevertheless, there are some differences among the measured and predicted 

flexural velocities at sensors 4 and 3 which are relatively far away from the source 

location. 

In order to explore the possible causes for the differences, the measured and 

computed flexural velocity at all sensors are plotted in Figure 18 and Figure 19, 

respectively. The measured data at all sensors except sensor 3 show the energy decay 

to some extent with the distance to the source. While the data at sensor 3 looks 

unreasonably high which are above the data at sensor 4 almost over the whole 

frequency range. The EnFlow result demonstrates the clear energy decay phenomena 

due to damping for all sensors with the distance of sensors to the source. One reason 

could be related to measurement error. Since the signal is getting weaker as the 

sensor location move further away from the sources the measurement error may have 

been increased due to higher background noise. The measured data at sensor 4 and 

sensor 3 may be affected more by the background noise. 

0.000001

0.00001

0.0001

0.001

0.01

0.1

1

40 60 80 100 120 140 160

Frequency (kHz)

Velocity (in/sec)

Location 13

Location 7

Location 6

Location 1

Location 5

Location 4

Location 3

Figure 18. Measured Flexural Velocity at All Sensors 
 - 13 -

0.0000001

0.000001

0.00001

0.0001

0.001

0.01

0.1

1

40 60 80 100 120 140 160

Frequency (kHz)

Velocity (in/sec)

Location 13

Location 7

Location 6

Location 1

Location 5

Location 4

Location 3

Figure 19. Flexural Velocity from EnFlow at All Sensors 

Typically, acoustic emission data is in very high frequency range where the elastic 

wavelength is very small and the vibration behavior is highly sensitive to the 

structural detail. These characteristics make using conventional finite element method 

impractical. Comet/EnFlow, which is developed based on the high frequency energy 

finite element method (EFEM), is a suitable tool for this type of analysis. Especially, 

comparing to the other high frequency tool, the governing equations of EFEM is 

directly derived from the wave propagation model which can predict well the 

vibration variation over the structure subject to acoustic emission type of sources. 
REPORT DOCUMENTATION PAGE Form Approved

OMB No. 0704-0188

2. REPORT TYPE 

Contractor Report

 4. TITLE AND SUBTITLE

Calibration of International Space Station (ISS) Node 1 Vibro-Acoustic 

Model

5a. CONTRACT NUMBER

NNL07AA00C

 6. AUTHOR(S)

Zhang, Weiguo; Raveendra, Ravi

 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

NASA Langley Research Center 

Hampton, Virginia 23681 

 

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National Aeronautics and Space Administration

Washington, DC 20546-0001

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NASA

13. SUPPLEMENTARY NOTES

This work was performed by Comet Technology Corporation for Science Systems and Applications, Inc., under NASA 

contract NNL07AA00C. 

Langley Technical Monitor: Eric I. Madaras

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14. ABSTRACT

Reported here is the ability of utilizing the Energy Finite Element Method (E-FEM) to predict the vibro-acoustic sound fields 

within the International Space Station (ISS) Node 1 and to compare the results with actual measurements of leak sounds made 

by a one atmosphere to vacuum leak through a small hole in the pressure wall of the Node 1 STA module during its period of 

storage at Stennis Space Center (SSC). While the E-FEM method represents a reverberant sound field calculation, of 

importance to this application is the requirement to also handle the direct field effect of the sound generation. It was also 

important to be able to compute the sound fields in the ultrasonic frequency range. This report demonstrates the capability of 

this technology as applied to this type of application. 

15. SUBJECT TERMS

Acoustics; Finite element method; International Space Station

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