A robust chisel damper for quieting a jackhammer is presented. The noise produced from a jackhammer chisel is dominated by the ringing of the chisel moil resulting from impacts of the internal hammer against the end of the chisel producing airborne radiation of the transverse bending and longitudinal modes. A model steel chisel moil point was constructed with geometric properties similar to a jackhammer chisel and designed so as to not fail during severe acceleration impacts from the reciprocating hammer. Anechoic tests of the maximum overall unweighted sound pressure level for the undamped chisel due to a longitudinal impact was 86.8 dB linear (re. to 20 μ Pa) at 1 meter with the strongest ring tone at 1.37 kHz and harmonics; the overall sound pressure level for the damped chisel with identical axial impacts was reduced by 16.5 dB to 70.3 dB with severe reduction of 40 dB of the dominant chisel ring tone, and the harmonics.

As an effort to reduce energy consumption and hazardous emissions, lightweight design has become more and more important for new vehicle developments. Substituting conventional steel material with other low-density materials in building vehicle structures is one typical approach for lightweight designs. To investigate the influence of the structural weight change on the noise, vibration and harshness (NVH) performance, this study presents a structural-acoustic coupled model of a rectangular shaped cavity enclosed by 1 or 2 flexible panels. Using this modal, parametric studies aiming at reducing the total structural weight and simultaneously improving the NVH performance are conducted. For the case of a single flexible panel subject to a point force excitation, it is found that substituting the heavier steel panel with a lighter Al panel may actually reduce the sound radiation inside the cavity at the low frequency range. On the other hand, at higher frequencies, the noise radiation level is roughly inversely proportional to the material density. For the case with dual flexible panels, although it is predicted that the two panels are weakly coupled through the acoustic cavity at most frequencies, the noise level may still be reduced at a lighter structural weight in certain cases.

The circular cylinder pipe is extensively used for the supplement of the gas. The leakage of this gas induces the catastrophic problem when it leases into open area in the city without any monitoring. A correlation method has been mostly used for the detection of the leakage. It is needed a good coherence and an efficient energy transmission to the external sensors for the reliable estimation of the correlation. This paper investigated theoretically the propagation of the acoustic wave of the circular cylinder pipe containing the gas in a pipe for the development of the leakage monitoring system. The acoustic wave is propagated through the waveguide of the circular pipe with the characteristics acoustically coupled by the gas contained in a cylinder and the shell. However, as a special case, the acoustic waves in a metal pipe containing gas are corresponded closely to the uncoupled in-vacuo shell waves and to the rigid-wall duct fluid waves. In this case, the dominant acoustic energy can be estimated at the frequencies in which coincidence between the shell modes and the acoustic modes occurs. In the paper, the characteristics of the dominant waves are theoretically investigated and analyzed experimenttally with a long steel pipe. The measured data is clearly analyzed by the continuous wavelet transform and by spectral density analysis.

A New finite element sandwich plate is presented. It is based on discrete displacement approach and allows for both symmetrical and unsymmetrical configurations. The validity and accuracy of the presented element is assessed through comparisons with both tests and classical FE modeling. The tests consist of various configurations of sandwich panels in a coupled plate-cavity system. A parametric study, using the developed element, is finally presented to highlights the effects of skin and core properties on the vibration and radiation of such structures under both airborne and structure-borne excitations.