共查询到20条相似文献,搜索用时 31 毫秒
1.
A laboratory setup and a procedure for measuring the volume coefficients and mean cross sections of extinction, scattering, and absorption of soot particles in the medium of saturated water vapor are described. A method for hydrophilization of the surface of soot particles, which makes it possible to obtain model objects with specified hygroscopic properties, is presented. The processes of transformation of soot particles are analyzed with the use of data of electron-microscopic investigations on the basis of the fractal approach. The structural parameters of hydrophobic soot are shown to depend on the conditions of moistening, whereas hydrophilic particles are subject to substantial structural changes indicative of their watering. Investigation of the coagulation of soot particles with drops shows that hydrophobic particles form a weakly bound system; they coagulate on the surface of drops and cause no changes in the structure of soot aggregates. During the coagulation, hydrophilic soot particles penetrate inside a drop and irreversibly form a mixed system. 相似文献
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A correlation log is a type of sonar system used for measuring the velocity of a surface vessel or of a submersible vehicle. The operation is similar to that of a conventional echo sounder, and the direction of acoustic propagation is vertically downwards. Since a correlation log can be used for either bottom tracking or water tracking, it is of interest to relate the transmitted power level to the echo levels from both bottom and volume scatterers, which is a means of predicting the log's performance. This is done by modeling the transmission channel in terms of the sonar equations 相似文献
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Emin Demirbağ Hülya Kurt Doğa Düşünür Kerim Sarıkavak Suna Çetin 《Marine Geophysical Researches》2007,28(4):343-353
In this study we made a comparative interpretation of multibeam bathymetric and seismic reflection data with different resolutions
and penetration properties collected in the Central Basin of the Marmara Sea. Our main objectives were (i) to investigate
and compare the active tectonic deformation observed on the sea bottom and within the uppermost sedimentary layers to that
of the deep-seated deformation within the limits of resolution and penetration of the available geophysical data and (ii)
to build a three-dimensional (3D) block diagram of the active tectonic and buried features by means of a sliced mapping technique. In this approach, we produced slice maps of the active and buried structural features at selected depths and then combined
them to form a 3D structural block diagram. Motivation for our work was to produce a 3D structural diagram to derive a more
detailed image of the structural features in the Central Basin where there is no available 3D seismic data. The observations
from the bathymetry and seismic data and developed 3D diagram support the presence of a through-going strike-slip fault that
forms a rotational depression zone against a right-stepping strike-slip faulting causing a pull-apart basin in the Central
Depression zone. 相似文献
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A. E. Gledzer E. B. Gledzer A. A. Khapaev Yu. L. Chernous’ko 《Izvestiya Atmospheric and Oceanic Physics》2014,50(2):122-133
Results of experiments are considered for flows generated by different sources-sinks of mass in the rotating annular channel with beta-effect simulation using the inclined bottom. Diagrams of regimes are presented in parameters of the dimensionless angular velocity of the zonal flow averaged over the channel width and the dimensionless angular velocity of transport of vortex perturbations of cyclonic and anticyclonic types. In experiments and the simplest linear theories, most attention is paid to diagram regions with a slow motion of vortices relative to the rotating coordinate system near the parameters for stationary Rossby waves. 相似文献
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Li Yanbao Song Reng
Associate Professor Dept. of Hydralulic Eng. Tianjin University Tainjin .
Professor Dept. of Hydralulic Eng. Tianjin University Tainjin 《中国海洋工程》1996,(2)
The analysis of the data of model tests of two large deep wharves and monographic experimental studies show that two aspects are to be improved so as to predict the wave uplift forces on the bottom of a circular cylinder. The first aspect is the uplift pressure distribution on the bottom, and the second is the correct determination of the phase for maximum horizontal wave forces. The second problem has been solved. Synthesizing the results of theoretical analysis and experiments, we suggest a diagram for the determination of the phase when the maximum horizontal wave force appears. On the basis-ef the diagram the simultaneous wave uplift forces can be obtained for the structural stability analysis. 相似文献
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A spectral range of 920 to 960 cm?1 is chosen for satellite measurements of the CO2 content in the atmosphere with a correlation method. The optimal transmission function of the measured gas in the correlation channel of the radiometer is estimated. It is shown that the effects that atmospheric gases (H2O, CO, O3, N2O, and CH4) and errors in specifying the land-surface temperature and the vertical air-temperature distribution have on errors in measuring the CO2 content throughout the entire atmospheric thickness may reach several percent. 相似文献
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This paper investigates the structural properties of a model fluid dictated by an effective inter-particle oscillatory potential by grand canonical ensemble Monte Carlo (GCEMC) simulation and classical liquid state theories. The chosen oscillatory potential incorporates basic interaction terms used in modeling of various complex fluids which is composed of mesoscopic particles dispersed in a solvent bath, the studied structural properties include radial distribution function in bulk and inhomogeneous density distribution profile due to influence of several external fields. The GCEMC results are employed to test the validity of two recently proposed theoretical approaches in the field of atomic fluids. One is an Ornstein--Zernike integral equation theory approach; the other is a third order + second order perturbation density functional theory. Satisfactory agreement between the GCEMC simulation and the pure theories fully indicates the ready adaptability of the atomic fluid theories to effective model potentials in complex fluids, and classifies the proposed theoretical approaches as convenient tools for the investigation of complex fluids under the single component macro-fluid approximation. 相似文献
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Hu Yunchang Li Xiangjing Zhang Lianying
Professor Dept. of Ocean Engineering Naval Architecture Tianjin University Tianjin Master Dept. of Ocean Engineering Naval Architecture Tianjin University Tianjin Doctor Lecturer Dept. of Ocean Engineering Naval Architecture Tianjin University Tianjin 《中国海洋工程》1998,(1)
In this paper the simple generation algorithms are improved.According to the geometricmeaning of the structural reliability index,a method is proposed to deal with the variables in the standardnormal space.With consideration of variable distribution,the correlation coefficient of the variables andits fuzzy reliability index,the feasibility and the reliability of the algorithms are proved with an example ofstructural reliability analysis and optimization. 相似文献
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The fatigue assessment plays an increasing role for the offshore structural safety. Many fatigue assessment methods have been developed for this purpose. Among those methods, the time domain method is regarded as the most accurate method but less adopted in practice due to time consuming. In order to improve the efficiency of the time domain method, an innovative block partition and equivalence method of the wave scatter diagram is developed for offshore structural fatigue assessment. After the wave scatter diagram is partitioned into several blocks, the newly developed method, involves determination of the equivalent wave height, wave period and occurrence probability of the representative sea states based on modified energy equivalent principle. The equivalent wave period of the representative sea state is calculated via the spectral moment formula in which the equivalent spectral moments of zero and second order are obtained based on the weighted averaging principle. Combining with the determined wave period, the equivalent significant wave height can be determined by reversing the wave spectrum integral formula, where the equivalent wave energy of a divided block of the wave scatter diagram is modified by introducing a factor to compensate the effect of low- and high-amplitude cycles fatigue damage. The equivalent occurrence probability is equal to the summation of the original sea states’ occurrence probability within the divided block. The developed method has the advantage of preserving the stochastic characteristics of the short term sea states within the divided block during determining the representative sea state. At the same time the newly developed method has no limitation on block partition and can be applied on different offshore structure. Two structural models, a fixed mono-pile platform and a floating semi-submersible platform, are demonstrated in the numerical examples. Results indicate that the newly developed method is robust, computationally affordable, and accurate within engineering expectations. 相似文献
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Coupled SPHS–BEM method is proposed for transient fluid–structure interaction problems: SPH shell (SPHS) is selected to discretize shell structures, the second-order doubly asymptotic approximations (DAA2) of boundary element method (BEM) is chosen to analyze flow-field. BEM can remedy the expensive costs for three-dimensional SPH (smoothed particle hydrodynamics), yet SPHS provides a structural solver for BEM. The coupled method is attractive, since only a layer of SPHS particles and a piece of flow-field boundary elements are needed to be modeled; the compatibility conditions of the coupled surface are performed with moving least square (MLS) function. The final two benchmarks on underwater impacts prove the feasibility, stability and accuracy of the proposed method. 相似文献
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海洋事件离不开各要素环境数据的共同作用,获取要素之间的关联关系从而进行海洋事件的预报预测,是一个亟待解决的问题。为此,本文提出一种多视图协同的关联关系分析方法来度量海洋各要素数据间的关联关系。首先,在传统平行坐标技术的基础上增加刷技术、轴排序等功能对海洋多要素数据进行初步探索,同时引入散点矩阵图展示各要素的分布;其次,以平行坐标中数据线间的角度、面积以及散点图中要素分布的距离为差异度量方式,对计算得到的差异构建相似性矩阵;再次,采用多维标度法得到原始多要素数据在低维空间中的表达;最后,使用K-means算法对降维后的低维度数据进行聚类分析。本文提出的方法从视觉角度对数据进行分析和特征挖掘,并得到高维数据在低维空间上的可视化展示,实现了有效量化海洋数据不同要素间的相关关系。 相似文献
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State-of-the-art process-based models have shown to be applicable to the simulation and prediction of coastal morphodynamics. On annual to decadal temporal scales, these models may show limitations in reproducing complex natural morphological evolution patterns, such as the movement of bars and tidal channels, e.g. the observed decadal migration of the Medem Channel in the Elbe Estuary, German Bight. Here a morphodynamic model is shown to simulate the hydrodynamics and sediment budgets of the domain to some extent, but fails to adequately reproduce the pronounced channel migration, due to the insufficient implementation of bank erosion processes. In order to allow for long-term simulations of the domain, a nudging method has been introduced to update the model-predicted bathymetries with observations. The model-predicted bathymetry is nudged towards true states in annual time steps. Sensitivity analysis of a user-defined correlation length scale, for the definition of the background error covariance matrix during the nudging procedure, suggests that the optimal error correlation length is similar to the grid cell size, here 80–90 m. Additionally, spatially heterogeneous correlation lengths produce more realistic channel depths than do spatially homogeneous correlation lengths. Consecutive application of the nudging method compensates for the (stand-alone) model prediction errors and corrects the channel migration pattern, with a Brier skill score of 0.78. The proposed nudging method in this study serves as an analytical approach to update model predictions towards a predefined ‘true’ state for the spatiotemporal interpolation of incomplete morphological data in long-term simulations. 相似文献
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A computational method for diagnosing three-dimensional atmospheric fronts from temperature, wind, and geopotential fields
on a three-dimensional regular grid is proposed. The criterion, which serves for the diagnosis of atmospheric fronts, is discussed.
The weights of the input information about the mentioned fields are optimized based on the maximal difference between the
correlation functions for (a) pairs of particles separated by the front and (b) pairs from one synoptic mass. These weights
were different for different baric levels. The correlation functions and the optimization of weights were estimated on the
basis of the archive of fields of the NCEP objective analysis on the half-degree latitude-longitude grid and data from aerological
observations. The results of numerical experiments on the construction of atmospheric fronts are presented. Applying the described
method to fields predicted for a term of up to 36 h showed that errors in the prognostic models introduce a relatively weak
distortion into the geometry of atmospheric fronts. 相似文献
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根据烟尘气溶胶的尺寸分布参数和消光系数,分析了烟尘气溶胶粒子数浓度与传输距离对链路衰减的影响。结合幅值阻尼信道对信道容量、信道保真度及信道误码率进行数值仿真。仿真结果表明,当传输距离为3 km,烟尘气溶胶粒子数浓度由2.1×106 m-3增加到3.2×106 m-3时,链路衰减由0.30 dB增加到0.46 dB,误码率由0.008 7增加到0.012 2。由此可见,烟尘气溶胶对星地量子通信的各项性能均有影响,且影响程度不一。仿真结果可为烟尘气溶胶影响下的量子信号传输提供参考。 相似文献
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Nelson E. Martins Srgio M. Jesus 《Oceanic Engineering, IEEE Journal of》2006,31(3):646-656
A blind estimator of the ocean acoustic channel impulse response envelope is presented. The signal model is characterized by a deterministic multipath channel excited by a highly nonstationary deterministic source signal. The time-frequency (TF) representation of the received signal allows for the separation between the channel and the source signal. The proposed estimator proceeds in two steps: First, the unstable initial arrivals allow for the estimation of the source signal instantaneous frequency (IF) by maximization of the radially Gaussian kernel distribution; then, the Wigner-Ville distribution (WV) is sequentially windowed and integrated, where the window is defined by the previously estimated IF. The integral gives the channel impulse response envelope, which turns to be an approximation to the blind conventional matched filter (MF). The blind channel estimator (CE) is applicable upon the following conditions: that the multipath channel contains at least one dominant arrival well separated from the others, and that the IF of the source signal is a one-to-one function. Results obtained on real data from the INternal TIde Measurements with Acoustic Tomography Experiments (INTIMATE'96), where the acoustic channel was driven by an linear frequency modulation signal, show that the channel's envelope detailed structure could be accurately and consistently recovered, with the correlation of the estimates ranging from 0.796 to 0.973, as compared to the MF result 相似文献
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A computer correlation technique is described for comparing observed magnetic anomaly profiles to model profiles generated from a paleomagnetic time scale. A model is computed for a given spreading rate, divided into small segments, and each segment then compared to a corresponding unit of the data profile. Each model segment is systematically shifted and correlated with the data, and the resulting correlation functions are displayed in an offset-age diagram. Interpretation of this diagram reveals possible histories involving faulting or changes of spreading rate that may be overlooked by the visual method, and quantitative estimates of the uncertainties in the spreading rates may be made. 相似文献