### ASA 127th Meeting M.I.T. 1994 June 6-10

## 4pSAa11. Application of statistical energy analysis for vibration and
sound radiation prediction of multi-sectional cylindrical shells.

**Michael V. Bernblit
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*St. Petersburg Marine Tech. Univ., Lotsmanskaya St., 3, 190008, St.
Petersburg, Russia
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Statistical energy analysis (SEA) is a powerful tool for vibration and
sound radiation prediction at high and medium audio frequencies. The objective
of this work (SEA based) is to evaluate acoustic power radiated by a large
scale complex structure when its vibration is defined only within limited
surface area in the vicinity of broadband sources. A tested structure is
divided into a set of energy finite elements (EFEs) and power balance matrix
(PBM) equation is solved to obtain the ratio of EFEs rms normal velocity
components. Coefficients of the PBM equation derive from transmission,
radiation, and internal loss factors. Acoustic power radiated by the whole
structure is calculated as the sum of partial acoustic inputs of EFEs. Each
power input is determined by radiation efficiency and surface averaged normal
velocity of a structural element. This approach enables one to define
generalized radiation efficiency of the total structure which links acoustic
power and rms vibration of the specific EFE with preliminary measured or given
at ``drawing board studies'' vibration. Damping factors provide additional
information needed to study the effect of design variables on radiation
efficiency of a whole structure. A typical for aerospace and shipbuilding
multi-sectional structure comprising cylindrical rib-stiffened shells with
transverse partitions separating them was selected to utilize the developed
approach. One of cylindrical subsets was driven by a normal broadband point
force and its vibration was measured in one-third octave bands and averaged
over its surface area. Drops of surface averaged vibration levels between
structural elements were computed using PBM equation. Assuming omnidirectional
pattern of sound radiation the total acoustic power and far-field sound
pressure were calculated. It allowed one to evaluate the total structural
radiation efficiency. Radiation loss factors for ribbed cylindrical shells in
light (air) and heavy (water) acoustic media were investigated to obtain
reliable data for PBM coefficients. Experimental data were in a good agreement
with theoretical prediction.