ICASE COUPLING BETWEEN PLATE VIBRATION AND ACOUSTIC RADIATION
A detailed numerical investigation of the coupling between the vibration of a flexible plate and the acoustic radiation is performed. The nonlinear Euler equations are used to describe the acoustic fluid while the nonlinear plate equation is used to describe the plate vibration. Linear, nonlinear, and quasi-periodic or chaotic vibrations and the resultant acoustic radiation are analyzed. We find that for the linear plate response, acoustic coupling is negligible. However, for the nonlinear and chaotic responses, acoustic coupling has a significant effect on the vibration level as the loading increases. The radiated pressure from a plate undergoing nonlinear or chaotic vibrations is found to propagate nonlinearly into the far-field. However, the nonlinearity due to wave propagation is much weaker than that due to the plate vibrations. As the acoustic wave propagates into the far-field, the relative difference in level between the fundamental and its harmonics and subharmonics decreases with distance. 1Research was supported by NASA Langley Research Center under NAS1-19317. 2Research was supported by the National Aeronautics and Space Administration under NASA Contract Nos. NASl-18605 and NASl-19480 while the third author was in residence at the Institute for Computer Applications in Science and Engineering (ICASE), NASA Langley Research Center, Hampton, VA 236810001.
A re-examination of the non-linear interaction between an acoustic fluid and a flat plate undergoing harmonic excitation
In a recent study Nayfeh and Kelly [1] employed a direct renormalization procedure to evaluate the structural and acoustic response resulting from resonant harmonic excitation of a flat plate. Such a problem had been solved earlier by a method that employs two co-ordinate strainings. The present investigation begins by showing that the finite amplitude acoustic waves are described by the same relations in the cases of resonant and non-resonant excitation. An explicit criterion for the location of a shock is obtained, and it is proven that shocks form along a series of straight lines. A quantitative example depicts various spatial and temporal responses; some of these responses have not been evaluated previously. The distortion effects are explained in terms of self-refraction phenomena, and the results of the dual renormalization method employed earlier are shown to be incorrect in the vicinity of the shock. †
Impacts of climate and land use changes on flood risk management for the Schijn River, Belgium
Abstract Flooding is the most common natural disaster in Europe. Modern flood risk management relies not only infrastructure development but also on governmental and non-governmental actors applying legal, economic and communicative water management instruments. Within the European Union (EU), flood management closely relies on policy set at the EU and national levels. It is now recognized that a sound understanding of climate change is required in addition to current management by taking into account land use change and socio-political context, as climate and land use changes have major impacts on hydrological responses. This paper investigates the hydrological behavior due to urbanization under current and future climate scenarios of high summer and high winter rainfall for 20 sub-catchments of the Schijn River, located in the Flanders region near Antwerp, Belgium. As urbanization increases and existing rainfall-runoff models neglecting the specific behavior of urban runoff, a hydrological model was developed based on a basic reservoir concept and applied to the existing rainfall-runoff model (PDM) flow to examine the specific urban contribution. Results revealed that peak flow for urban runoff and the total peak flow (i.e. rural and urban runoff) were significantly higher (i.e. ranges from 200% to 500%) than the existing rainfall-runoff model (PDM) flows, because of faster and more peaked urban runoff response. The impact of climate change on current and future conditions was also assessed by estimating peak flows with respect to return periods from the flood frequency curve. The predicted peak flow of high summer future climate scenario was significantly higher (i.e. ranges from 200% to 250%) than that of the current climatic condition for this region. Furthermore, hourly peak flow and daily volume ratios of 100-year return period for the highest, lowest and average impervious area were projected for the time horizon of the year 2100. It is concluded that climate change impacts contribute the most in producing peak flow in coming years, while increased urbanization takes the second place for both hourly and daily values. Results on urbanization effect and climate change impact assessment are useful to the water managers for spatial planning, emergency planning and insurance industry.