共查询到17条相似文献，搜索用时 203 毫秒
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色散缓变光纤中脉冲频谱演变的研究 总被引：1，自引：0，他引：1
采用数值计算的方法研究了高斯脉冲的频谱在色散缓变光纤中的传输特性及初始啁啾对频谱演变的影响.结果表明:色散缓变光纤可以有效的抑制频谱的展宽,将其应用到超长距离光纤通信系统是可行的;初始啁啾使脉冲频谱严重展宽,应采取消啁啾的措施. 相似文献
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通过数值解非线性耦合薛定谔方程 ,研究高速光孤子通信系统中高阶色散和偏振模色散对孤子传输的影响 ,并数值模拟孤子在单模光纤中的演变。研究结果表明 :偏振模色散导致孤子脉冲展宽、峰值功率下降、峰值点随传输距离漂移 ;高阶色散和偏振模色散使孤子加速展宽、脉冲沿出现非对称的振荡结构 ,脉冲峰值点随传输距离的漂移而发生改变 相似文献
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从非线性薛定谔方程出发,采用分步傅立叶分析方法数值模拟光子晶体光纤中超连续谱的产生,计算、模拟并分析初始啁啾在光子晶体光纤的零色散点对超连续谱演变和带宽的影响.结果表明,非线性作用使频谱分裂成多峰不对称的结构,初始啁啾C的引入能明显的改善超连续谱的带宽和平坦性.由于二阶色散β2=0,三阶色散猹对超连续光谱的展宽影响较大.当β3>0时,C取正值时,随着C的增大,带宽减小; C取负值时,带宽有所增大,平坦性也有改善;β3<0时,无论C取正取负,频谱带宽增大,且平坦性较好. 相似文献
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建立具有色散性的水平二维非线性波浪方程,方程的非线性近似到了三阶。方程以波面升高和自由表面速度势表达的微分-积分型数学方程,给出方程的数值求解方法和算例,对方程积分项的处理给出了计算方法。计算结果与Boussinesq方程模型和缓坡方程模型的对应计算结果进行了对比。 相似文献
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基于有限差分法建立高阶Boussinesq方程的一维数值模型,时间步进上采用三阶预报、四阶校正格式。在验证数值模型适用性的基础上研究了坡度、水深和波高对孤立波分裂位置、主峰和次峰波高大小的影响,证明了孤立波的分裂与非线性特征有关。坡度缓,非线性演化的时间长,孤立波更易分裂,但坡度变缓不会明显增强波浪非线性特征,从而对主、次峰波高影响不大;入射波高大、水深浅(深水水深或浅水水深)的孤立波非线性特征更强,波形更尖锐,孤立波更易发生分裂,且主、次峰波高也越大。 相似文献
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Recent extensive and important studies have provided detailed information and compelling evidence on how the presence of waves influences the vertical diffusivity/dispersivity in the coastal environment, which can affect various water quality considerations such as the distribution of suspended sediments in the water column as well as the potential of eutrophication. Comparatively, how the presence of waves influences the horizontal diffusivity/dispersivity has received only scant attention in the literature. Our previous works investigated the role played by the Taylor mechanism due to the wave-induced drift profile which leads to the longitudinal dispersion of contaminants in the horizontal direction, under regular sinusoidal waves and random waves with single-peak spectra.Natural waves in the coastal environment, however, often possess dual-peak spectra, comprising both higher frequency wind waves and lower frequency swells. In this study, the Taylor dispersion of contaminants under random waves with dual-peak spectra is examined through analytical derivation and numerical calculations. The effects of various dual-peak spectral parameters on the horizontal dispersion, including the proportion of lower frequency energy, peak frequency ratio and spectral shape parameter, are investigated. The results show that the relative energy distribution between the dual peaks has the most significant effect. Compared with single-peak spectra with equivalent energy, the Taylor dispersion with dual-peak spectra is stronger when the lower frequency is close to the peak frequency of the single-peak spectrum, and weaker with the higher frequency instead. Thus, it can be concluded that with a dual-peak wave spectrum, wind-dominated seas with higher frequency lead to stronger dispersion in the horizontal direction than swell-dominated seas with lower frequency. 相似文献
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Hidekazu Yasuda 《Journal of Oceanography》1983,38(6):385-394
The longitudinal dispersion effect due to the boundary layer formed by a tidal oscillatory current is examined theoretically. This analysis reveals the process whereby the dispersion coefficient becomes steady after the release of the diffusing substance. Though the dispersion due to an oscillatory current has so far been investigated mostly in the case of a linear velocity profile, the following result was found by taking account of the boundary layer in the oscillatory current. The depth-averaged dispersion coefficient for the case of a current having a boundary layer can be a few times larger than in the case of a linear velocity profile when the characteristic mixing time is long; the phase lead in the boundary layer induces nearly 20 percent of the longitudinal dispersion effect. 相似文献
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The directional spreading of both the wavenumber and frequency spectra of finite-depth wind generated waves at the asymptotic depth limit are examined. The analysis uses the Wavelet Directional Method, removing the need to assume a form for the dispersion relationship. The paper shows that both the wavenumber and frequency forms are narrowest at the spectral peak and broaden at wavenumbers (frequencies) both above and below the peak. The directional spreading of the wavenumber spectrum is bi-modal above the spectral peak. In contrast, the frequency spectrum is uni-modal. This difference is shown to be the result of energy in the wind direction being displaced from the linear dispersion shell. A full parametric relationship for the directional spreading of the wavenumber spectrum is developed. The analysis clearly shows that typical dispersion relationships are questionable at high frequencies and that such effects can be significant. This result supports greater attention being focussed on the routine recording of wavenumber spectra, rather than frequency spectra. 相似文献
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Hidekazu Yasuda 《Journal of Oceanography》2004,60(3):587-596
The fundamental nature of the mass flux due to the shear effect is examined analytically in a basin with steady and oscillatory
currents to promote a better understanding of the mass transport process in coastal waters. The currents are given from solutions
of the simplified motion equation so as to be consistent with the diffusion equation. The matter concentration used is given
by an analytical solution of the diffusion equation with the settling flux term contained. Mass flux, yielding the depth-averaged
dispersion coefficient, is rather varied vertically in both steady and oscillatory currents. In the oscillatory current with
a Stokes layer in particular, the vertical profile of flux is more complicated and even negative flux is induced near the
basin floor. This negative flux does not necessarily yield a negative value of the vertically averaged dispersion coefficient.
The exact dispersion coefficient given by the flux analysis is realized only in the steady state of the matter concentration
distribution, though we can scarcely observe the steady state in the actual sea. The vertically uniform longitudinal dispersion
coefficient at the stationary stage is shown to be caused from the vertical complexity of mass flux by the action of the vertical
diffusing and the settling flux.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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M. Vantorre 《Ocean Engineering》1986,13(4)
An investigation of the hydrodynamic behaviour of bodies in a large-amplitude oscillatory motion, for example in view of wave power absorption by floating bodies, not only requires the knowledge of added mass and damping coefficients, which can be calculated by means of a linear theory, but also of higher-order forces. Especially the third-order values will have to be calculated, because they contain a first-harmonic component.A computation procedure has been developed in order to calculate hydrodynamic forces up to the third order, acting on axisymmetric bodies in an oscillatory heaving motion. The method only requires the knowledge of first- and second-order potential functions, even for the calculation of third-order forces.Experiments have been carried out on floating conical and submerged cylindrical models, in order to evaluate the theoretical procedure. 相似文献
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Hidekazu Yasuda 《Journal of Oceanography》1998,54(2):151-164
An analytical method for describing horizontal matter dispersion in shear currents is presented using a tensor expression
from the point of view that matter dispersion due to the shear effect should be one of the principal mixing dilution processes.
Although the behavior of horizontal dispersion is considerably more complicated than common longitudinal dispersion, the present
study elucidates the vertical structure of dispersion and the dispersing process from the initial to the stationary stage,
besides the usual depth-averaged dispersion coefficient at the stationary stage. As one of the typical applications of horizontal
dispersion, dispersion due to the pure drift current with an Ekman layer is examined theoretically using the present method.
This examination reveals that the displacement of the centroid and the major axis of dispersion are twisted in the vertical
direction more than the direction of the current vector forming the Ekman spiral; that the variance increases in proportion
to the third power of the elapsed time; and that the dispersion coefficient at the stationary stage remains constant, independent
of the depth normalized by an Ekman layer thickness. Such dependence of the dispersion coefficient in the steady current is
shown to be different from that in the oscillatory current, which is inversely proportional to the depth normalized by a Stokes
layer thickness. This is considered to be induced by the difference of the vertical profiles of the first order moment in
both currents, that is, the shear region of the first order moment is restricted around the floor by the alternation of the
current shear in the oscillatory current while it is diffused in the whole depth in the steady current. 相似文献
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针对不规则波浪作用下Wigley型船的运动响应问题进行了系统的研究,采用统计学方法深入探讨了船舶不规则运动幅值和响应周期的分布规律,并通过傅里叶变换对船舶运动响应进行了频谱特征分析。结果表明,船舶横摇方向与升沉和纵摇方向随机运动的响应特征有显著差异。在升沉与纵摇方向,波浪谱峰频率远离自振频率,前十分之一大振幅运动对应周期离散性较小,基本稳定在波浪谱峰周期附近,但小振幅运动周期分布离散性较大,频谱分析指出船舶升沉与纵摇运动响应频谱在波浪谱峰频率附近出现明显峰值。而在横摇方向,波浪谱峰频率与自振频率相耦合,不同振幅的横摇运动响应周期均稳定在自振周期附近,且周期离散性较小,频谱分析也表明横摇运动响应频谱主要集中于船舶运动自振频率附近。 相似文献