Numerical modeling of a flexural displacement-converter mechanism to excite a flat acoustic source driven by piezoelectric stack actuators

This paper studies an acoustic source with a relatively small thickness and high bending stiffness. The acoustic source operates in the low frequency, quasi-static regime. The focus of the current study is on the actuation part in order to design an appropriate excitation mechanism. A flexural mechanism is modeled in combination with piezoelectric actuators to convert an in-plane displacement of the actuators to a perpendicular out-of-plane direction. First, an optimization simulation is used to determine the size of the required piezoelectric actuator. Then an equivalent electrical circuit of the lumped acoustic source is developed. This equivalent circuit can directly be connected to the electrical model of a switching amplifier. Finally, a coupled numerical finite element analysis is carried out by using COMSOL Multiphysics software package to model the combination of both flexural mechanism and piezoelectric device. The suggested flexural mechanism is sufficiently narrow to overcome the space limitation challenge in the design

Active control of a lumped acoustic source driven by various actuators

This paper studies an acoustic source with a relatively small thickness and high bending stiffness. The high bending stiffness is obtained with a sandwich structure in which the face of the sandwich structure internal to the source is perforated to increase the acoustic compliance. Multiple actuators are used to drive the moving component of the acoustic source. Feedback and feedforward damping control techniques are used to actively obtain a smooth frequency response, especially at low frequencies. Such a compensation scheme generally leads to amplification of the lower frequencies and may result in a significant electrical input power. In addition, a part of the input power is stored in mechanical and acoustical elements of the acoustic source. Voice coil and piezoelectric actuators are compared regarding the ability to recover the stored energy. Piezoelectric actuators are particularly attractive from energy recovery point of view because the acoustic source has to operate in the low frequency, quasi-static regime. The two-way energy ?ow between the actuator and a connected ampli?er is investigated. In particular, the effectiveness of energy recovery from the reactive components of the acoustic source is evaluated to improve the overall radiation ef?ciency. A lumped model is used to represent the acoustic source that is excited by a stacked piezoelectric element. The required power supply and resulting radiation ef?ciency are evaluated when a conventional analogue ampli?er is used. The result is compared to the case in which some parts of the stored power are recovered and sent back to the connected switching amplifier. It was found that approximately 66% of the reactive power stored in the acoustic source can be recovered. The study also reveals a significant increase in overall system ef?ciency and more than 80% decrease in the amount of required input power through recovering the reactive power in the system

Building an integrated modeling framework for assessing land-use change and its consequences for areal water balance in mountainous Southwest China

The opening up of China's industry towards market orientation has a distinct impact on natural resources as well as on social structures. The example of rubber introduction in Yunnan province (SW China) shows the mutual interdependencies between economy, natural resources, and social structures. We assess the impacts of rubber introduction and possible development paths in the study area. An integrated modeling framework (NabanFrame) is developed for the catchment of the Naban River (size 270 km2), a tributary to the Mekong River. NabanFrame comprises an agro-economic, ecological, and social model. Altogether they interact with a land-use change model via defined interfaces. Effects on the water cycle are considered by additionally integrating the spatially distributed rainfall-runoff and water balance model AKWA-M® in the model framework. Therefore, a reasonable parameterization is needed to assess the land-use changes on areal water fluxes. The authors conclude that the chosen hydrological model is able to assess the impacts of land conversion (from forest to rubber plantations) on catchment hydrology and address further adaptations to be implemented in the hydrological model.BMBF/LILA

Implementation issues of a high-speed distributed multi-channel ADDA system

ABSTRACT A multi-channel ADDA controller is used in many active noise cancellation and active vibration control problems. Such a controller is able to yield good performance, however it also requires a lot of hardware on a centralized place and a lot of sensitive wiring. A practical work around for this problem would be to use a local single channel controller. However such a controller would reduce the overall system performance and may introduce instability. In this paper a system will be presented that acts as a hybrid form and combines the performance of a local feedback loop with a large multi-channel controller. To reduce the wiring and the influence of disturbances on this wiring a local analog to digital and digital to analog converter will be used. These systems will be interconnected using a high-speed serial communication system. To reduce the sample rate for the overall system, a local decimation and interpolation filter will be implemented. Further performance improvements will be realized by means of a simple local feedback system. The implementation issues concerning such a system are the subject of this paper

Evolution of surface gravity waves over a submarine canyon

The effects of a submarine canyon on the propagation of ocean surface waves are examined with a three-dimensional coupled-mode model for wave propagation over steep topography. Whereas the classical geometrical optics approximation predicts an abrupt transition from complete transmission at small incidence angles to no transmission at large angles, the full model predicts a more gradual transition with partial reflection/transmission that is sensitive to the canyon geometry and controlled by evanescent modes for small incidence angles and relatively short waves. Model results for large incidence angles are compared with data from directional wave buoys deployed around the rim and over Scripps Canyon, near San Diego, California, during the Nearshore Canyon Experiment (NCEX). Wave heights are observed to decay across the canyon by about a factor 5 over a distance shorter than a wavelength. Yet, a spectral refraction model predicts an even larger reduction by about a factor 10, because low frequency components cannot cross the canyon in the geometrical optics approximation. The coupled-mode model yields accurate results over and behind the canyon. These results show that although most of the wave energy is refractively trapped on the offshore rim of the canyon, a small fraction of the wave energy 'tunnels' across the canyon. Simplifications of the model that reduce it to the standard and modified mild slope equations also yield good results, indicating that evanescent modes and high order bottom slope effects are of minor importance for the energy transformation of waves propagating across depth contours at large oblique angles

ATIVS: analytical tool for influenza virus surveillance

The WHO Global Influenza Surveillance Network has routinely performed genetic and antigenic analyses of human influenza viruses to monitor influenza activity. Although these analyses provide supporting data for the selection of vaccine strains, it seems desirable to have user-friendly tools to visualize the antigenic evolution of influenza viruses for the purpose of surveillance. To meet this need, we have developed a web server, ATIVS (Analytical Tool for Influenza Virus Surveillance), for analyzing serological data of all influenza viruses and hemagglutinin sequence data of human influenza A/H3N2 viruses so as to generate antigenic maps for influenza surveillance and vaccine strain selection. Functionalities are described and examples are provided to illustrate its usefulness and performance. The ATIVS web server is available at http://influenza.nhri.org.tw/ATIVS/