In general, modern acoustic modeling techniques such as Statistical Energy Analysis (SEA), Ray-tracing techniques, and Finite Element Methods have been used effectively to reduce interior noise in automotive, aircraft, and some spacecraft designs. Each method has its own strengths depending on the type of noise being modeled and the assumptions used, but it is clear that these methods have been effective; automotive and aircraft noise levels have been substantially reduced in recent years. Also, the continued development, current sophistication, and rising sales of off-the-shelf acoustic modeling software are indicative of their applicability and success; otherwise the companies that build automobiles and aircraft would not purchase these. See Reference 1 for a recent article describing the state of the art in acoustic modeling capabilities, including off-the-shelf acoustic modeling software tools.

The objective of this project will be to develop an acoustic modeling capability, based on off-the-shelf software, to be used as a tool for oversight of the future manned spaceflight vehicles to ensure compliance with acoustic requirements and thus provide a safe and habitable acoustic environment for the crews.

Reference

1. von Estorff, Otto, “NUMERICAL METHODS IN ACOUSTICS: FACTS, FEARS, FUTURE,” 19th INTERNATIONAL CONGRESS ON ACOUSTICS, Madrid, September 2007.

• Observed great utility and capability of the Statistical Energy Analysis (SEA) acoustic modeling method both in the accuracy of the results (in the applicable frequency range), and in the geometrical complexity that can be accommodated.

• Reversed the Orion team decision to push back (up) the Orion cabin noise limit.

• Prompted the formation of the Orion Acoustic Working Group for resolving Orion cabin acoustics related issues.

• Prompted Lockheed Martin to hire a vibro-acoustics engineer for crew module (CM) cabin acoustic environment modeling and analysis.

• Developed Level 2 requirements for the CM Snorkel Fan and the Waste Management System. The Snorkel Fan requirement is to limit pre-launch and post-landing Speech Interference Levels.

• Initiated a collaborated effort with Lockheed Martin staff for Orion CM cabin acoustic environment modeling and analysis. The findings described in this report were provided to Lockheed Martin staff, helping to promote and validate similar system-level noise treatments for the actual Orion vehicle. This resulted in the acceptance of a mass allocation for the system-level noise treatments, which were then assigned to various Orion system teams for implementation.

For the ISS US Lab mockup, three mockup interior reverberant environments were modeled and validated successfully using single and dual airborne sound sources with known sound power levels. Two methods were developed to model the mockup interior absorption: one was based on the measurement of mockup interior reverberation time; the other was based on impedance tube measurement of sound absorptive material used to cover the interior surfaces of the mockup. The effect of source location on the accuracy of the model predictions under a highly absorptive mockup interior was observed. Furthermore, strategy was developed to model the SPL distribution in a large mockup with a highly absorptive interior.

The modeling of the Orion CM acoustic mockup involved more complex geometrical shape and ventilation fan with unknown sound power levels beforehand. Sound power levels of the ventilation fans were estimated from sound intensity measurements. The fidelity of the mockup and the model were increased from an empty interior in the beginning to include an ECLSS (Environmental Control and Life Support System) wall and ECLSS bay with open/sealed gaps between the ECLSS wall and the mockup wall. There were two configurations of sound absorptive Thinsulate attached to the surfaces of the ECLSS wall panels. An effective method of deploying sound absorptive material in reducing cabin SPL was discovered by modeling and validated by measurement. The effect of sealing the gaps to prevent noise from leaking into the cabin was also modeled and validated. Lastly, a bare Orion CM mockup with aluminum interior walls was also modeled and validated. The purpose of the study was to increase the mockup interior reverberation time to the level typical of a spacecraft pressure vessel interior.

Also, lessons were learned regarding the problem of absorption coupling between adjacent cavities, e.g., cabin and ECLSS bay in the CM mockup, and the problem of Damping Loss Factor sensitivity when modeling structure-borne noise.

In general, modern acoustic modeling techniques such as Statistical Energy Analysis (SEA), Ray-tracing techniques, and Finite Element Methods have been used effectively to reduce interior noise in automotive, aircraft, and some spacecraft designs. Each method has its own strengths depending on the type of noise being modeled and the assumptions used, but it is clear that these methods have been effective; automotive and aircraft noise levels have been substantially reduced in recent years. Also, the continued development, current sophistication, and rising sales of off-the-shelf acoustic modeling software are indicative of their applicability and success, otherwise the companies that build automobiles and aircraft would not purchase these. See reference 1 for a recent article describing the state of the art in acoustic modeling capabilities, including off-the-shelf acoustic modeling software tools.

The objective of this project will be to develop an acoustic modeling capability, based on off-the-shelf software, to be used as a tool for oversight of the future manned spaceflight vehicles to ensure compliance with acoustic requirements and thus provide a safe and habitable acoustic environment for the crews.

1) The acoustic modeling method was validated regarding important secondary structure, e.g. closeout panels. In particular, the acoustic transmission properties of the Orion secondary structure partition (that separates the crew habitable volume from the environmental control system’s fans and pumps) was modeled and mocked-up inside the Orion Acoustic Mockup with a realistic fan noise source located behind the partition. The predictions and measurements were in good agreement, thus validating the modeling approach. In addition to the panel validation, transmission loss modeling representation of acoustic blocking materials was validated against the model’s “mass law” representation.

2) In collaboration with the Orion Prime Contractor, a detailed acoustic model of the Orion Crew Module version 606h was developed. Later in the year this model was collaboratively updated to revision 606g, the latest version of the full-capability Orion Crew Module. This model was used to advocate the development of “system-level” noise treatments (see below) to aide in the global reduction of noise levels in the Crew Module. The benefit of this approach was to enable development of “component noise allocations” that the fan and pump developer could achieve in order to meet the acoustic requirements.

3) Finally, the Acoustic Modeling Project made recommendations of noise treatments, specifically the acoustical sealing of gaps around the closeout partition (mentioned above) and the addition of acoustically absorbent treatments to some surfaces inside the Crew Module. These noise controls were modeled and mocked-up in the Orion Acoustics Mockup and their acoustical advantages were validated. This information, along with further modeling of noise control trade studies, acoustic flight-materials investigations, and implementation studies (performed by Orion Prime) were presented to management in order to obtain mass-budget of 35 lbs, and hardware ownership of the noise treatments in order for their implementation.

As a result of the above achievements, the prospect of the Orion Crew Module meeting the stringent acoustic requirements has been greatly increased.

In general, modern acoustic modeling techniques such as Statistical Energy Analysis (SEA), Ray-tracing techniques, and Finite Element Methods have been used effectively to reduce interior noise in automotive, aircraft, and some spacecraft designs. Each method has its own strengths depending on the type of noise being modeled and the assumptions used, but it is clear that these methods have been effective; automotive and aircraft noise levels have been substantially reduced in recent years. Also, the continued development, current sophistication, and rising sales of off-the-shelf acoustic modeling software are indicative of their applicability and success, otherwise the companies that build automobiles and aircraft would not purchase these. See reference 1 for a recent article describing the state of the art in acoustic modeling capabilities, including off-the-shelf acoustic modeling software tools.

The objective of this project will be to develop an acoustic modeling capability, based on off-the-shelf software, to be used as a tool for oversight of the future manned Constellation vehicles to ensure compliance with acoustic requirements and thus provide a safe and habitable acoustic environment for the crews. During FY’07, the project’s first year, this project:

1. Determined the acoustic modeling requirements for Constellation vehicles, in terms of frequency range, source type, and model type, and leased an off-the-shelf software package that is well-suited for the modeling task.

2. Developed a simple-geometry acoustic model and validated the model using a physical mockup and acoustic measurements. Tools for modeling the effects of absorptive wall treatments and the resulting reverberation environment were developed as part of this work. Limitations of the modeling technique were also investigated and documented.

• Modified the acoustic reverberation time of the CM mockup to match the reverberation time inside the ISS US Lab in the speech bands, i.e. 0.5, 1, 2, and 4 kHz, for evaluating CM Snorkel Fan noise on post-landing crew communications. Thinsulate© sound absorption material was attached to the interior surface of the mockup to achieve this purpose. An SEA acoustic model of the CM mockup was used to predict the amount of acoustic treatment required, and reverberation time measurements were made to verify the match to the desired reverberation environment.

• Validated the SEA model in predicting mockup interior SPLs (Sound Pressure Levels) due to the emissions of realistic ventilation fan sources. The sound power levels of these fan sources were unknown a priori. Sound power levels of these fan sources were estimated using a sound intensity measurement technique. This is opposed to prior studies where a RSS (Reference Sound Source) with known calibrated sound power was used.

A measurement grid system of rectangular box shape was built for sound intensity measurements. The grid system enclosed the source to be measured with five surfaces, i.e., front, right, back, left, and top. Sound intensity at the center of each segment of the grid system was measured and time averaged for 15 sec. Sound intensity at the bottom surface reflected most of the incident sound energy so that it was accounted for at the other measured surfaces. Non-stationary background noise of the Chamber was of concern because it could introduce some net error on estimated fan sound power. The technique of estimating sound power via sound intensity measurements can cancel out only stationary background noise sources outside the grid system.

Acoustic testing was performed in the Orion CM mockup, and comparisons were made with acoustic modeling predictions. The comparisons showed very good agreement, plus or minus 3 dB above the Schroder frequency (where SEA is expected to give good results). The case studied was very realistic as the sound absorption material covered only part of the wall (i.e., 30% of the area of conical and vertical wall). The effect of such sound absorption material was predicted by:

• mockup cavity absorption predicted from measured mockup interior reverberation times and then using Sabine equation, or

• a two-layered Thinsulate© layup model, which attaches to the face (i.e., the interior wall surface) of the mockup cavity. The lay-up model was developed based on the results of impedance tube absorption testing. Furthermore, the effect of air absorption, which is notable in high frequencies (> 1 kHz), was also included.

Currently, the mockup only includes the bare pressure shell. The development of a fairly high-fidelity ECLS wall closeout panel was completed in FY’09. Installing the closeout panel into the mockup, updating the mockup acoustic model with the closeout panel, and validating the model with sound pressure measurement in the mockup will be performed.

In addition to the modeling development described above, other significant achievements were made with respect to Orion acoustics work. In particular, the Orion acoustic mockup, built as part of this acoustic modeling project, was used in demonstrations to protect the acoustic requirements (and the resulting Orion crew acoustic environment). Hamilton Sundstrand had indicated that the acoustic requirements were too strict and that they were not going to meet them. This included the continuous noise requirement, and the noise requirement for the Snorkel Fan (used after landing in a contingency situation). The Orion acoustics mockup was used to demonstrate to high level CxP management what the effects of higher noise levels would mean to Orion crews. As a result, a new commitment was made to hold to the acoustic requirements. An Acoustic Noise Control Plan will now be developed, and additional resources are being used to control noise during design of the vehicle. As part of this effort, the Snorkel Fan noise requirement was re-evaluated and updated to ensure adequate crew voice communications during a contingency landing situation.

In general, modern acoustic modeling techniques such as Statistical Energy Analysis (SEA), Ray-tracing techniques, and Finite Element Methods have been used effectively to reduce interior noise in automotive, aircraft, and some spacecraft designs. Each method has its own strengths depending on the type of noise being modeled and the assumptions used, but it is clear that these methods have been effective; automotive and aircraft noise levels have been substantially reduced in recent years. Also, the continued development, current sophistication, and rising sales of off-the-shelf acoustic modeling software are indicative of their applicability and success, otherwise the companies that build automobiles and aircraft would not purchase these. See reference 1 for a recent article describing the state of the art in acoustic modeling capabilities, including off-the-shelf acoustic modeling software tools.

The objective of this project will be to develop an acoustic modeling capability, based on off-the-shelf software, to be used as a tool for oversight of the future manned Constellation vehicles to ensure compliance with acoustic requirements and thus provide a safe and habitable acoustic environment for the crews. During FY’07, the project’s first year, this project:

1. Determined the acoustic modeling requirements for Constellation vehicles, in terms of frequency range, source type, and model type, and leased an off-the-shelf software package that is well-suited for the modeling task.

2. Developed a simple-geometry acoustic model and validated the model using a physical mockup and acoustic measurements. Tools for modeling the effects of absorptive wall treatments and the resulting reverberation environment were developed as part of this work. Limitations of the modeling technique were also investigated and documented.