The project will have two major objectives:
1) Optimize the effectiveness of the TNAP for 2nd generation and other pile-driving scenarios.
2) Model underwater pile driving noise attenuation as a function of distance from the pile and compare with measurements.

1. Two masters level students have joined the project. The first joined in September 2008 and the second in March 2009.

2. A PhD level student has been recruited and will join the project in September of this year.

3. An investigation of the damping of the TNAP pipes has been completed. It has been concluded that damping surface treatment of the TNAP pipes will only be effective in damping frequencies about 2000 Hz. Lowering the noise levels above 2000 Hz will not result in a significant decrease in overall noise levels since the vast majority of the energy of the pile noise is below 1000 Hz. We have therefore recommended to not surface treat the pipes with damping material. We are of the opinion that it would have a marginal acoustic effect and not be justified by the added cost of manufacturing the TNAP.
4. The Vashon TNAP design has been finalized. Technical drawings of the final design have been completed and submitted to WFS. Follow up communications with WFS and the contractor regarding the TNAP fabrication is continuing.
5. Our first experimental investigation of the sound propagation from a pipe has been completed. The goal of this experiment was to identify the resonant frequencies that are responsible for sound radiation, to verify the accuracy of our numerical model, and to determine the effect of damping. The corresponding mode shapes were identified with the help of a finite element model of the pipe. The natural frequencies obtained from the finite element model were in close agreement with the experimental values. The sound radiation from the pipe treated with damping paint and damping sheets was compared to the untreated pipe. It was shown that the damping treatments are only effective in damping high frequency modes over 2,000Hz. However, our aim is to reduce noise below 1,000 Hz. We will therefore not rely on structural damping of the TNAP to obtain its desired sound transmission performance.
6. A numerical investigation of the behavior of the deformation of a pile subjected to impact loading using transient analysis with the finite element package COMSOL is underway. The goal here is to develop a detailed understanding of how displacement in the pile produces acoustical radiation. A snapshot of the wave propagation in a pile after it has been impacted is shown in Figure 1. This figure shows several well defined wave fronts and the stress field behind the wave fronts. The finite element model now allows us to predict the resulting sound
pressure levels in the surrounding water.
Figure 1. Stress propagation in a pile a short time after impact.
The simulation requires significant computing power since the rapidly traveling wave front requires a small time step for accuracy. In addition, the number of degrees of freedom of the finite element model is large due to need do mesh the surrounding water in addition to the pile. We are therefore planning to use the 18 machine parallel processing cluster at Department of Mechanical Engineering for the prediction of the sound pressure level at distances larger than 1 meter.
7. A numerical finite element model that includes the TNAP has been initiated using COMSOL.
8. A detailed analysis of the pile driving sound data collected by WSDOT during WSF Mukilteo Test Pile Project, November 2006 has been conducted. This work is now complete and will be presented in a master thesis this summer. Figure 2 show a comparison of the sound energy levels at ten meters of a pile with and without a TNAP.
9. The design of scaled experiments the examine the acoustic radiation from pipes and shielded pipes and to evaluate the accuracy of the finite element models using APL’s test barge facility on Lake Union has been completed. The experiments will be conducted during an August-September time window.

Planned work for the next six month:

1. The first experiments using APL’s fully instrumented test barge facility will be conducted on Lake Union during an August-September time window (approximately 3 days). Acoustic radiation from scaled piles with and without an acoustic shield will be examined. The barge will be used regularly to investigate the effectiveness of a range of noise control techniques to shed more light on the physics of acoustic radiation of shock loaded structures and to verify the completeness and accuracy of our structure/acoustic models.

2. The finite element modeling of the submerged pile with the TNAP will be continued.

3. We will model the sound radiation from piles in shallow water. The modeling will be accomplished by numerical simulation through the use of the parabolic wave equation numerical code. We will utilize acoustic modeling specifically for the Vashon site and the results from the simulations will be compared to field test data in order to the tune the model and to evaluate its accuracy. The goal of this approach is to produce a model that can yield accurate results for any future shallow water pile driving site.

4. The feasibility of developing lighter and more readily deployable versions of the TNAP will be investigated.

5. A new PhD student will be initiated to the project in September.

6. Interaction with WFS and the contractor regarding the TNAP fabrication will continue.

7. Data will be gathered by Jim Laughlin at WSDOT and (our) UW team during pile driving as part of the Vashon ferry terminal Dolphin replacement project scheduled to be initiated during the month of November 2009, and the UW team will take the lead in data analysis.

8. The effectiveness of the TNAP treatment will be evaluated by the use of the Vashon field test data.

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Second Progress Report, June 2009
The goal of this project is to evaluate the effectiveness of a modified Temporary Noise Attenuation Pile (TNAP) to reduce the underwater sound level from pile driving operations.
The project objectives are:
1) Design of the TNAP that is going to be used during the 2009 field trial at the Vashon ferry terminal.
2) Work with WSDOT/WFS in field testing of the full-scale TNAP as part of the 2009 Vashon Ferry Terminal project, including analysis of data.
3) Measure and model shallow water sound propagation so that it will be possible to predict the sound levels at distances of up to 500 m from the pile.
4) Optimize the effectiveness of the TNAP for second generation and other pile-driving scenarios.