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10 CHAPTER 2 Research Approach Task 1. Analyze Literature, cle, and then were conducted with trucks performing a series Research, and Current Practice of passby procedures. Beamforming measurements were con- ducted for a number of test configurations. A review was conducted of current noise source identifica- The proof-of-concept test data were post-processed and tion techniques. Emphasis was on beamforming, which had analyzed in a laboratory. This analysis included an experimen- been demonstrated to be generally suitable for this type of tal evaluation of various performance characteristics of the measurement. A major objective of the literature review was to array measurement system, comparison with the theoretical quantify frequencies, distances, array sizes, etc., to ensure that parameters specified earlier for the array in the design stage, as the array developed for this project would reflect the current well as example results for truck passbys at low- and high-speed state of the art. The recent work by I&R for Caltrans provided tracks with localization and identification of individual noise key data for analysis of these issues, particularly for investigat- sources for the tested trucks. ing array size, frequency range, and spatial resolution. Results of the review of current noise source identification techniques are presented in Chapter 3. Task 4. Submit Interim Report The interim report summarizing the results of Tasks 1 Task 2. Develop Experimental Design through 3 was submitted in July 2007. It presents the results of the literature search, development of the experimental design, Two separate experimental tasks were proposed in this project to develop a practical measurement technique for and the proof-of-concept tests. Following a review and meet- quantifying truck noise sources. The first experimental task ing with the NCHRP, comments by the NCHRP were accom- was the design and validation of a noise source mapping tech- modated in the experimental design and testing plan for the nique through proof-of-concept tests on a limited number of remaining tasks. Work on the subsequent tasks proceeded fol- trucks and pavements, with emphasis on validating the noise lowing NCHRP approval. mapping method. This proof-of-concept test was completed in Tasks 2 and 3 and is described in Chapter 3. Task 5. Execute Testing Plan The second experimental task of the project, application of Task 3. Perform Proof-of-Concept the validated method to quantify noise sources on typical Test heavy trucks, was accomplished through noise mapping of a The technology demonstration was accomplished through number of trucks under actual roadside conditions on an in- the proof-of-concept testing with the assistance of Inter- service highway. Prior to the mapping, the necessary adjust- national Truck and Engine Corporation (IT) at their proving ments to the technique identified during the proof-of-concept grounds in Fort Wayne, Indiana, in July 2006. A limited but testing of Task 3 were performed. The roadside testing was representative sample of trucks was selected from the vehicle conducted in April 2008 with the beamforming system collect- test matrix developed in the previous task and available at IT. ing data for a wide range of trucks and various operating con- The beamforming tests were conducted on a stationary truck ditions on a selected highway (US 301). One hundred vehicle operating under different conditions, were validated using passbys were recorded in one day of testing using the measure- known sound sources such as loudspeakers added to the vehi- ment system developed.