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<p>The  transition  matrix,  relating  the  scattered  and  incident  acoustic  waves for  a  thin  elastic  spherical  shell  in  a  free-field  environment,  has  been evaluated  using  the  ATILA  finite-element  code.  A  three-dimensional finite-element  model  of  a  0.5-m  outer  radius,  1-cm  thick  spherical  steel  shell surrounded  by  water  was  developed.  The  ATILA  code  was  used  to  calculate the  scattered  pressure  over  the  surface  of  the  shell  for  incident  waves represented  as  products  of  radial  Hankel  functions  and  spherical  harmonics. The  chosen  driving  frequency  was  474  Hz,  corresponding  to  a  value  of  ka=  1, where  k  is  the  wavenumber  of  sound  in  water  and  a  is  the  radius  of  the  shell. The  ATILA  results  were  compared  with  the  results  of  analytical  thin  shell theory,  and  were  found  to  agree  for  a  model  which  divided  the  spherical shell  surface  into  72  approximately  equal  area  triangular  regions.  Also computed  for  each  component  was  the  modal  acoustical  impedance  of  the shell.  These  results  agreed  within  two  percent  for  the  zeroth  order component  and  thirteen  percent  for  the  first  order  components.
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<br>Subjects: NA</div>
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Costa Ruiz, Arthur Lobo da</div>
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