Radiative forcing of aerosols and gases over tropical ocean and its impact on the global atmospheric environment: GCM investigations during INDOEX campaigns

Radiative forcings due to aerosols and the pollutant gases accumulated as haze which are transported from nearby continent to the tropical ocean are essentially important elements of the world climate system. Vertical transport of aerosols and gaseous species takes place within the deep convective cloud clusters of the inter-tropical convergence zone and subsequently these are distributed by the upper atmospheric zonal wind flow, thereby have impact on the global atmospheric environment. The comprehensive global atmospheric models have shown capability of simulating the climate of the atmosphere with proper forcing. We have deduced the radiative forcing, optical depth and the global energy balance components by a global atmospheric model. The results are validated well with INDOEX and other available observational findings.     

An inversion modelling method to obtain the acoustic power of the noise sources in a large factory

A common problem for large factories that wish to decrease their environmental acoustic impact on neighbouring locations is to find out the acoustic power of every noise source. As these factories cannot stop their activity in order to measure each source individually, a procedure is needed to obtain the acoustic powers with the factory under normal operating conditions. Their contribution to the overall sound pressure level at each neighbouring location can then be found and it is possible to calculate the improvements obtained after any modification of the sources. In this paper an inversion modelling method is used to do so. Acoustic powers are obtained by means of field sound pressure level measurements and with the use of a sound propagation software. A careful analysis of the solution has been carried out by simulating errors on the measured data in order to detect possible correlations between the acoustic power of different sources and avoid misleading interpretations of the results. The whole methodology has been applied to a liquid-gas production factory.     

穿孔板在切向流条件下非线性效应的理论与实验研究

流过声衬表面的切向流和高声压级的声场对于穿孔板共振结构的声学特性有这非常显著的影响。本文从波涡相互作用机制出发,发展了一种旨在研究矩形穿孔板在切向流条件下非线性效应的离散涡模型。同时用双传声器法测量了不同几何参数的穿孔板的声阻抗随偏流速度及声压级的变化情况。将本文的实验与理论结果进行了对比分析,对比的结果表明本文的实验与理论结果符合良好。     

球体二层海内波中一阶波浪力计算

球体在水下运动时会受到内波对其产生的作用力，从而产生大幅度的垂荡和纵摇运动，影响其操纵性。但这一方面的研究还很不成熟，本文利用边界元法计算了二层流体中球体在典型内波作用下受到的一阶垂荡波浪力和一阶纵摇波浪力矩，并利用此方法计算了近水面球体的波浪力及力矩，与已有的计算结果和水池实验结果比较，吻合较好。     

五阶双色双向海洋表面波理论

将经典的"纯波动的三阶单色单向Stokes波理论"提升至"可包含环境均匀流效应的有限水深五阶双色双向海洋表面波理论".亦即,在已有三阶双色双波理论的基础上得到了自由表面位移、速度势和非线性振幅色散关系的第四阶、第五阶显式表达式.从中,将居于核心地位的"双色双向波的第五阶非线性振幅色散关系"又推广到"无穷多波中任意两两不同频率不同振幅相互作用波的非线性振幅色散关系".针对双色双向短峰波的典型特性,以若干个图表详加示之.     

Objective estimation of the tuning features of historical carillons

The carillons of the Mafra National Palace are undergoing a restoration project. Together, the pair of carillons represent the largest surviving 18th century carillons in Europe. To guarantee the historical significance of these outstanding musical instruments, a detailed diagnosis of their current physical tuning state was achieved and results were analyzed with respect to historical, acoustical and musical concerns. In a first stage, we developed a suitable polyreference modal identification technique to infer the tuning status of bells from their modal parameters and we then systematically performed in-field modal testing experiments on a selection of historical bells of the Mafra carillons. For each carillon bell, tuning charts displaying the internal frequency relationships between its most important partials were obtained, as well as the mode shapes, decay times and beating frequencies between modal-doublets for every single musical partial of the bell. In a second part, since carillon bells also must be tuned very accurately one relative to the others in order to play in tune, the important topic of estimating the reference pitch and musical temperament of carillons was addressed by devising optimization techniques, here tentatively based on the actual modal frequencies of the bells. After presenting the modal identification procedure and optimal strategies developed for this work, the feasibility and interests of this instrumental approach are finally illustrated for the two carillons of Mafra.     

Physics-based modeling techniques of a twelve-string Portuguese guitar: A non-linear time-domain computational approach for the multiple-strings/bridge/soundboard coupled dynamics

The Portuguese guitar is a pear-shaped instrument with twelve metal strings which is widely used in Portuguese traditional music. Unlike most common guitars, it has a curved top-plate and a specific violin-like bridge which is not rigidly fixed to the soundboard of the instrument. From the dynamical point of view, if the bridge transmits the strings vibrations to the instrument body in order to maximize the radiated energy, it also couples all the component parts of the instrument which therefore interact by structural coupling. This can originate various audible effects such as beating behavior and the excitation of numerous sympathetic resonances enhanced by the large number of strings of the instrument, and this is certainly why the Portuguese guitar has such distinct sound compared to other guitars. In this paper, a fully coupled time-domain model of the Portuguese guitar is developed and a series of simulations are presented to emphasize the various coupling phenomena involved in sound production. To reproduce the main musical features, the model includes the coupled dynamics of the twelve strings supported by a bridge which interact with the body of the instrument, described through Finite-Element modeling of the soundboard of a typical Portuguese guitar. Further simple models have been devised for the string/fret interaction and the pluck excitation. Since nonlinear effects are quite apparent in the behavior of string musical instruments, the string dynamics is modeled by the Kirchhoff–Carrier equations which describe large-amplitude string vibrations, and includes the coupling between both polarizations of string motion. The coupling between the strings and the soundboard at the bridge is provided by a model of the bridge kinematics, built on the basis of simple geometrical rationale, so that the two perpendicular string motions can exchange energy back and forth. By a close examination of the energy transfers between the various subsystems of the model, we first assess the correct behavior of the physical model and then examine the respective influence of the string nonlinearity and the bridge on the nonplanar motion of the string. The fully coupled model which pertains to the restricted group of studies which deals with the complete physical-based modeling of a multi-stringed instrument, captures many important phenomena observed in practice, among which the pitch glide effect and the mutual excitation of sympathetic vibrations.     

Analytic ray curve tracing for outdoor sound propagation

Outdoor sound propagation, which propagates sound through inhomogeneous, moving media with complex obstacles, presents challenging scenarios for computational simulation. In this paper, we present a ray-tracing method that uses analytic ray curves as tracing primitives in order to improve the efficiency of outdoor sound propagation in fully general settings. This ray-curve tracer inherits the efficiency and flexibility of rectilinear ray tracers in handling boundary surfaces, and it overcomes the performance limitations imposed by approximating the curved propagation paths in inhomogeneous media with rectilinear rays. Adaptive media traversal, as well as acceleration structures for surfaces intersections, lead to further savings in computation. Our method’s speedup over existing ray models, at least an order of magnitude for simple 2D scenarios and up to two orders of magnitude for 3D complex scenes, is demonstrated on outdoor benchmark scenes.     

Approximate method for obtaining source quantities for calculation of structure-borne sound transmission into lightweight buildings

An approximate approach is described, for obtaining the source quantities required for the calculation of structure-borne sound power from machines into supporting lightweight building elements. The approach is in two stages, which are based on existing international Standards for measurement. The first stage involves direct measurement of the source free velocity at each contact, to give the sum of the square velocities. The second stage is based on the reception plate method and yields the single equivalent blocked force, which approximates the sum of the square blocked forces. The applicability of the source data obtained has been investigated in a case study of a fan unit on a timber joist floor. The approach contains several significant simplifying assumptions and the uncertainties associated with them are considered. For the case considered, the power transmitted into the floor is estimated by the approximate method to within 5 dB of the true value, on average.     

Identification of fish vocalizations from ocean acoustic data

A new method for identification of fish vocalizations based on auditory analysis and support vector machine (SVM) classification is presented. In this method, high resolution features have been extracted from fish vocalization data using the amplitude modulation spectrogram (AMS) of the input signals to facilitate the identification of grunts and growls made by a highly vocal wild fish, Porichthys notatus. The comparison results made from ocean audio recordings verify the effectiveness of the proposed method in identifying various types of fish vocalizations. The relationships between signal-to-noise ratio (SNR) and ocean temperature with the accuracy of the proposed method have also been quantified. Moreover, a context-aware prediction algorithm is introduced for estimating the continuous data.