Ships and other ocean structures have components, which are thin planar or
curvilinear viscoelastic solid layers surrounded by air or water. The present work deals with the
identification of material parameters of these layers to extend the scope of the real-time
structural health monitoring. The work proposes the approach to the parameter identification from
passive sensing of acoustic signals resulting from the operational load. The identification is
based on the partial integro-differential equation (PIDE) for the non-equilibrium part of the
average normal stress. The PIDE is derived in the work. It includes the Boltzmann
superposition integral associated with the stress-relaxation function. It is shown that, in the
exponential approximation for this function, the PIDE expresses the steady-state solution (with
respect to a certain variable) of the corresponding third-order partial differential equation (PDE)
of the Zener type. The operat- ors of both the equations are identical. The equations are
applicable at all values of the stress-re- laxation time. The roots of the characteristic equation
of this operator are consistently analyzed, and the acoustic attenuation coefficient for arbitrary
high frequencies is indicated.
The approach is exemplified with the identification of the layer-material stress-relaxation time
and ratio of the bulk-wave speed to the layer thickness. This identification can be carried out
from the acoustic acceleration normal to the layer measured by an acoustic
accelerometer attached to the layer surface and is applicable to both planar and
curvilinear layers. The identification method presumes the finite-difference calculation of the
time derivatives of the measured acoustic acceleration up to the third order and can be computationally efficient