### ASA 124th Meeting New Orleans 1992 October

## 3pSA3. Transient propagation in a finite one-dimensional pipe: Direct
temporal calculation and experiment.

**J. Dickey
**

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G. Maidanik
**

**
K. Crouchley
**

**
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*David Taylor Res. Ctr., Annapolis, MD 21402
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*
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The temporal response of a long (~100-ft) pipe is calculated and measured.
The calculation is based on a formalism that describes a complex of coupled
one-dimensional dynamic systems [J. Acoust. Soc. Am. 89, 1--9 (1991)]. The
flexural, longitudinal, and torsional waves in the pipe are considered as
separate systems in the model and interact only at discontinuities; the ends of
the pipe in this case. In the experiment, the pipe is subjected to an impact
that excites all three types of propagation and the response is measured by an
accelerometer mounted on the outside of the pipe, or, in the case when the pipe
contains water, by a hydrophone inside the pipe. In the model, the excitation
is simulated by forming initial wave packets in each of the three systems, and
the relative amplitudes of the initial excitations in the systems are
adjustable parameters. Other adjustable parameters include the reflection
coefficients of a particular wave type, the coupling between wave types at the
ends of the pipe, and the wave speeds and losses in the systems. The calculated
response versus time is assessed in the flexural wave system (assuming that
this is the only wave type which the accelerometer responds to), or in the
fluid system when present, and compared with the experimental data and the
model parameters are adjusted for an optimal fit. Once the model parameters are
optimized, the adjustable parameters can be deduced and the model can be
extended to more complicated situations. The noninteraction of the mode types
propagating in the systems is a basic premise in the model and is violated in
the fluid filled case since the fluid wave is strongly coupled to the
structural waves; nevertheless, the model shows qualitative agreement in this
case and good agreement for the air-filled case. The model also includes the
dispersive nature of the flexural wave propagation and demonstrates the
complexity in the response which develops over time but which ultimately
simplifies into a model pattern.