海洋表面波的3-4-5波共振守恒理论

面对海洋表面完整的两大波要素–-张力波和重力波, 构建出一个确定、丰富、基本的有限水深海洋表面波的“3-4-5波共振守恒理论”. 与以往经典、现代的多种结果相比, 充分保证了该理论的“精确性、对称性、完备性”, 为后继、普适的海洋波湍流统计理论提供了一个必备基础. 关键词： 海洋表面波 Hamilton描述 3-4-5波共振 波湍流     

Transmutation of non-local boundary conditions in ocean acoustics

We employ a transmutation technique to construct a new non-local boundary condition for the paraxial approximation in ocean acoustics. The transmutation operator introduced by De Santo and Polyanskii, when applied to the Helmholtz equation governing the acoustic pressure in the water column, leads to the so-called parabolic equation of Fock and Tappert. This transmutation operator acting on the N-D map at the water–bottom interface yields an intermediate non-local boundary condition for the parabolic equation which eliminates the backscattering terms in the Schwartz kernel of the N-D map. The kernel of the intermediate condition is approximated by a uniform stationary phase formula taking account of the possible coalescence of the brach points of the integrand with the stationary points of the phase, and it leads to a non-local boundary condition of Volterra-type for the parabolic equation. This condition is quite different than similar conditions derived by other approximations, in that the kernel of the Volterra operator is smooth, the smoothing effect coming from the fact that the horizontal range coordinate is scaled with the relative refraction index between the water column and the bottom.     

On heat and moisture exchanges between the sea surface and the atmosphere during the Medalpex

Summary Data collected by a buoy, moored in the Ligurian Sea about 27 nautical miles off the coast during the period 1 March-31 May, 1982, are analysed. The buoy was equipped by the Institute for Naval Automation (IAN) of the Italian National Research Council (CNR) during the Mediterranean Alpine Experiment (Medalpex), joint program of the Alpine Experiment (Alpex). Exchanges of heat and mass across the air-sea interface are computed from the collected data and comparisons with existing values are made. The resulting agreement confirms the strong interaction between the sea and the atmosphere in some peculiar situations, and lends weight to the oceanographic hypothesis for the statistical occurrence of deepening of orographic cyclones in the Liguro-Provencal basin. Paper presented at the IV Congresso del Gruppo Nazionale per la Fisica dell'Atmosfera e dell'Oceano, June 22–24, 1987, Rome.     

All-optical adaptive scanning acoustic microscope

We have constructed a fast laser-based surface acoustic wave (SAW) microscope, which may be thought of as a non-perturbing scanning acoustic microscope. The instrument is capable of rapid high resolution vector contrast imaging at several discrete frequencies, without any damage to the sample. Tailoring the generating optical distribution using computer-generated holograms allows us to both focus the acoustic waves (increasing their amplitude) and to spread the optical power over the sample surface (preventing damage). Accurate quantitative amplitude and phase (velocity) measurements and unique acoustic contrast mechanisms are possible with our instrument based on this technology due to the non-perturbing nature and the instrument geometries.However, the complexity of the optical generation profile leads to a strong dependence on material properties such as the SAW velocity and material anisotropy. We address these issues in this paper, and demonstrate how a spatial light modulator may be used to adapt the generating optical distribution to compensate for the material properties. This facilitates simpler alignment and velocity matching, and, combined with an acoustic wavefront sensor, will allow real-time adjustment of the generating source to enable imaging on anisotropic materials.     

Ripple damping on water surface covered by a spreading film: Theory and experiment

Summary The results of point-by-point laboratory dampingvs. frequency measurements using mechanically generated ripples on a water surface covered by monomolecular film of oleic alcohol are discussed in terms of a theory that takes into account coupling of Laplace and Marangoni modes.

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Riassunto Una teoria delle onde gravito-capillari alla superficie di acqua ricoperta da un film monomolecolare di spandimento, che tien conto dei modi di Laplace e di Marangoni, e del loro accoppiamento, è usata per guistificare delle misure di smorzamento ondoso effettuate in vasca con film di alcool oleico.

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Резюме В рамках теории, которая учитывает связь мод Лапласа в Марангони, обсуждаются результаты лабораторных измерений затухания в зависимотси от частоты. При измерения использовалась механически возбужденная рябь на поверхности воды, покрытой мономолекулярной пленкой олеинового спирта.

     

Wideband acoustic absorption characteristics of rubberized coir for underwater applications

Reflection and transmission coefficients of rubberized coir pads over the frequency band 200 kHz to 4 MHz are presented in this Paper. These results are compared with those reported for neoprene, paraffin wax, rubber car mat and plastic door mat¹. The rubberized coir pads were found to possess wideband absorption characteristics. It has been experimentally found that 0.05 m thick coir pads have almost 100% absorption in the frequency range 800 kHz-3 MHz with a maximum at 2.35 MHz. We have used this material for lining the water tank for underwater acoustic studies.     

Complex ray method and its applications to underwater acoustics

In this paper,the principle of complex source point and various analyt-ical methods of complex ray are summarized.Some possible applications ofcomplex ray method to underwater acoustics are proposed,including complexray analysis of directional acoustic fields,complex ray simulation of directivityof acoustic radiator arrays,complex ray transformation of acoustic fields fromnear zone to far zone,as wel1 as theoretical prediction of sonar target strengthby complex ray method.     

Influence of external tidal and meteorological forces on the bradyseismic phenomenon in the Phlegraean Fields

Summary Large tidal and meteorological influences on the present behaviour of the bradyseismic phenomenon in the Phlegraean Fields have been significantly determined. The two recent reinstatements of the uplift in 1970 and 1982 were found to be preceded by anomalous large increase of the mean oceanic loading. A significant covariance of the annual cycle of oceanic loading (and rainfall) with the number of shocks was also ascertained. Similarly it has been shown that the amplitudes and the significance level of the tidal terms in the number of shocks, related to extensional tidal stresses activing faulting, increase with the volcanic activity. Both these results indicate that oceanic loading (and rainfall) and tidal terms may contribute in warning the phenomenon. The tidal triggering is better explained as the effect of the product of each concurrent tidal component. Moreover, it is shown that the geophysical system in the area is getting more sensitive to the examined weak external forces and therefore becoming closer to unstable conditions. On the other hand, since the sea-level will certainly decrease in the near, future, a significant reduction of the volcanic activity is expected in the next months.

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Riassunto Nel presente lavoro si quantizza e si spiega l'influenza delle forze esterne meteomarine e mareali sulla evoluzione del fenomeno bradisismico in atto a Pozzuoli. Le recrudescenze del fenomeno nel 1970 e nel 1982 sono state precedute ad anomalo innalzamento, a periodo dell'ordine degli anni, nel livello medio del mare; cosí come sono state rilevate cospiranti variazioni annuali nel livello del mare, nella sismicità e nel sollevamento del suolo. Poiché pioggia e livello del mare sono strettamente legati non è stato possibile in questa fase dell'indagine una distinzione tra gli effetti delle due possibili concause sul fenomeno bradisismico, che comunque contribuiscono all'incremento del contenuto di acqua nelle rocce. è stato mostrato che l'ampiezza e la significatività delle onde mareali nel numero dei sismi crescono con l'aumentare dell'attività vulcanica. è stato anche mostrato che la probabilità di un evento sismico di piú elevata energia in una particolare ora connessa a date posizioni del sole e della luna è circa 3 volte maggiore rispetto ad altra ora pure predeterminabile. Si fornisce anche una possibile spiegazione dell'effetto degli stress mareali sull'attività sismica. Livello del mare e stress mareali possono perciò contribuire allo studio, della previsione dell'evoluzione del rischio sismico e vulcanico. Mentre da una parte l'accertata amplificazione delle onde mareali nei terremori del 1983 rispetto al 1970 lascia desumere che il sistema flegreo si approssimi a condizioni critiche, dall'altra il sicuro prossimo abbassamento del livello del mare lascia prevedere un'assai prossima e cospicua attenuazione del fenomeno in atto.

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Резюме Определяется большое влияние приливных и метеорологических сил на поведение орадисейсмического явления в Флегрчнных Лолях. Обнаружено, что двум недавним восстановлениям подъема в 1970 г. и в 1982 г. предшествовало аномально большое увеличение средней океанической нагрузки. Также установлена заметная ковариантность годового цикла океанической нагрузки (и осадков) с числом толчков. Показывается, что амилитуды и уровень значимости приливных членов увеличиваются с вулканической деятельностью. Оба этих результата указывают, что океаническая нагрузка (и осадки) и приливные члены могут давать вклад в предупреждение явления. Приливный спусковой механизм может быть объяснен, как эффект умножения для каждой приливной компоненты. Кроме того показывается, что геофизическая система в свободном пространстве является более чувст-вительной к исследованным слабым внешним силам и, следовательно, становится ближе к неустойчивым условиям. С другой стороны, т. к. уровень моря будет понижаться в ближайшем будущем, то ожидается заметное уменьшение вулканической деятельности в ближайшие месяцы.

     

基于BDRM理论的深海声场快速预报研究

深海存在深海声道和双轴声道两种典型环境，WKBZ简正波方法已实现了深海声道中声场的快速准确预报，而对于双轴海洋声道则存在一定的误差。本文在WKBZ本征函数的基础上，推导出了参考界面相位修正的一致表达式，并将浅海声传播的波束位移射线简正波（BDRM）理论应用于计算双轴海洋声道中的声场，进行了数值模拟并与传统简正波方法进行比较，结果表明应用BDRM理论计算的传播损失具有很高的精度和速度。