Method and apparatus for active cancellation of noise in a liquid-filled pipe using an adaptive filter

Abstract

An method and apparatus for active noise cancellation in a conduit carrying a liquid, employing a detector hydrophone, an acoustic canceler downstream of the detector hydrophone, an error hydrophone, and an adaptive filter. The outputs of the detector hydrophone, acoustic canceler, and error hydrophone are directed into the adaptive filter, which uses them to select the form of acoustic signal which the canceler directs into the liquid to cancel the noise. One embodiment of the invention employs two such cancellation circuits, and an additional adaptive filter which globally optimizes the cancellation of both circuits.

We claim: 
     
       1. An active noise cancellation system for a conduit carrying a liquid, said system comprising: a first detector hydrophone for detecting acoustic noise in said liquid;   a first acoustic canceler, downstream of said first detector hydrophone, for directing a first acoustic cancellation signal into said liquid;   a first error hydrophone for detecting acoustic signals downstream of said first acoustic canceler;   a first digital electronic adaptive filter;   a first means for imputing, said first means for imputing being effective to imput the outputs of said first detector hydrophone, said first acoustic canceler, and said first error hydrophone, into said first adaptive filter;   wherein said first adaptive filter is effective, responsive to said outputs of said first detector hydrophone, said first acoustic canceler, and said first error hydrophone, to drive said first acoustic canceler in a manner effective to minimize noise at said first error hydrophone according to a preselected local cost function;   wherein said system further comprises:   a second detector hydrophone for detecting acoustic noise in said liquid;   a second acoustic canceler, downstream of said second detector hydrophone, for directing a second acoustic cancellation signal into said liquid;   a second error hydrophone for detecting acoustic signals downstream of said canceler;   a second digital electronic adaptive filter;   a second means for imputing, said second means for imputing being effective to imput the outputs of said second detector hydrophone, said second acoustic canceler, and said second error hydrophone, into said second adaptive filter; and   wherein said second detector hydrophone is downstream of said first error hydrophone;   wherein said second adaptive filter is effective, responsive to said outputs of said second detector hydrophone, said second acoustic canceler, and said second error hydrophone, to drive said second acoustic canceler in a manner effective to minimize noise at said second error hydrophone according to a preselected local cost function; and   said system further comprising a master adaptive controller responsive to said first and said second error hydrophones for causing said first and second adaptive filters to globally minimize noise at said first and second hydrophones according to a preselected global cost function.   
     
     
       2. The system of claim 1, wherein: at least one of said means for inputing comprises: a bandpass filter for electronically filtering the output of said detector hydrophone, and an amplifier for amplifying the output of said detector hydrophone.   
     
     
       3. A method of noise cancellation in a system having a conduit carrying a liquid, said method comprising steps for: employing a first and second detector hydrophone for detecting acoustic noise in said liquid;   employing a first and second acoustic canceler for directing a responsive first and second acoustic cancellation signal into said liquid;   employing a first and second error hydrophone for detecting acoustic signals downstream of said a first and second canceler, respectively;   inputing the outputs of said first detector hydrophone, said first acoustic canceler, and said first error hydrophone, into a first adaptive filter, wherein said first adaptive filter is effective, responsive to the outputs of said first detector hydrophone, said first acoustic canceler, and said first error hydrophone, to drive said first acoustic canceler in a manner effective to minimize noise at said first error hydrophone according to a selected local cost function;   imputing the outputs of said second detector hydrophone, said second acoustic canceler, and said second error hydrophone, into a second adaptive filter, wherein said second adaptive filter is effective, responsive to the outputs of said second detector hydrophone, said second acoustic canceler, and said second error hydrophone, to drive said second acoustic canceler in a manner effective to minimize noise at said second error hydrophone according to a preselected local cost function; and   imputing the outputs of said first and second error hydrophone into a master adaptive controller effective to cause said first and second adaptive filters to globally minimize noise at said first and second hydrophones according to a preselected global cost function.   
     
     
       4. The method of claim 3, wherein: at least one of aid hydrophones used in at least one of said steps for employing a detector hydrophone comprises: a bandpass filter for electronically filtering the output of said detector hydrophone.   
     
     
       5. An active noise cancellation system for a conduit carrying a liquid, said system comprising: first and second detector hydrophones for detecting acoustic noise in said liquid;   first and second acoustic cancelers for directing respective first and second acoustic cancellation signals into said liquid;   first and second error hydrophones for detecting acoustic signals in said liquid;   first and second digital electronic adaptive filters;   first means for imputing effective to imput the outputs of said first detector hydrophone, said first acoustic canceler, and said first error hydrophone, into said first adaptive filter;   said first adaptive filter is effective, responsive to said outputs of said detector hydrophone, said first acoustic canceler, and said first error hydrophone, to drive said first acoustic canceler in a manner effective to minimize noise at said first error hydrophone according to a preselected local cost function;   said second adaptive filter is effective, responsive to said outputs of said second detector hydrophone, said second acoustic canceler, and said second error hydrophone, to drive said second acoustic canceler in a manner effective to minimize noise at said second error hydrophone according to a preselected local cost function; and wherein:   said first detector hydrophone, said first acoustic canceler, and said first error hydrophone are each upstream of each of said second detector hydrophone, said second acoustic canceler, and said second error hydrophone; and   said system further comprises a master adaptive controller responsive to said first and said second error hydrophones for causing said first and second adaptive filters to globally minimize nose at said first and second hydrophones according to a preselected global cost function.