Shake table tests of suspended ceilings to simulate the observed damage in the M_s 7.0 Lushan earthquake, China

Severe damage to suspended ceilings of metal grids and lay-in panels was observed in public buildings during the 2013 M7.0 Lushan earthquake in China. Over the past several years, suspended ceilings have been widely used practice in public buildings throughout China, including government offices, schools and hospitals. To investigate the damage mechanism of suspended ceilings, a series of three-dimensional shake table tests was conducted to reproduce the observed damage. A full-scale reinforced concrete frame was constructed as the testing frame for the ceiling, which was single-story and infilled with brick masonry walls to represent the local construction of low-rise buildings. In general, the ceiling in the tests exhibited similar damage phenomena as the field observations, such as higher vulnerability of perimeter elements and extensive damage to the cross runners. However, it exhibited lower fragility in terms of peak ground/roof accelerations at the initiation of damage. Further investigations are needed to clarify the reasons for this behavior.

Equivalent source method for identification of panel acoustic contribution in irregular enclosed sound field

For the interior sound field formed by the complex vibrating structure, an identifi- cation approach of panel acoustic contribution based on equivalent source method （ESM） was presented. The normal velocity on the surface of vibrating structure was first reconstructed by using interior nearfield acoustic holography based on ESM and the prediction of whole interior enclosed sound field was realized. Then the sound pressure produced by each panel at the interested field point was respectively replaced by the radiated pressure of the enclosed interior sound field which is formed by the equivalent virtual sources located near the surface of the cav- ity. Combining with the reconstructed normal surface velocity, the acoustic contribution of each panel to any position in the cavity was obtained by transforming the complex enclosed non-free field into the simple interior free field. Numerical simulations and experiments are conducted, and the influences of the number of the equivalent sources and the distance between them and the reconstructed surface have been investigated. The results show that the proposed method is easier to be implemented with the same accuracy than the traditional analysis method.

Prediction and validation of tonal noise from underwater propellers

Prediction and validation of low-frequency line spectrum noise from ship propeller under non-cavitating condition is presented.The flow field is analyzed with potential-based panel method,which requires the hydrodynamic forces to be integrated over the actual blade surface,rather than over the mean-chord surface.Then the pressure data is used as the input for Ffowcs Williams-Hawkings formulation to predict the far field acoustics.At the same time,propeller unsteady force is measured in hull-behind condition in China Large Cavitation Channel（CLCC）.Line spectrum noise of the 1st blade passage frequency（BPF） of a five-bladed propeller operating in a non-uniform flow field is got according to the calculated and measured unsteady forces,in which good agreement is obtained,and the 1st BPF noise difference is within 3.0 dB.The investigation reveals that prediction precision of the propeller＇s 1st BPF unsteady force with panel method have reached engineering practical degree,providing significant parameters for prediction of propeller line spectrum noise.