南沙群岛及其邻区低频和中频重力场的分离

建立了一个分离中、低频重力场的数学模型。根据南沙群岛地质构造的特征，选择4条具有代表性的重力测线N2，N9，N10和N11的自由空间重力异常，进行福里哀频谱值的计算并研究振幅谱值的分布规律，确定61.44km为4条重力测线的低频和中频重力场的临界值；设计分开低频和中频重力场的分离因子，分离出4条重力剖面的低频和中频重力异常；进而分析其低频和中频重力异常的特征。结果表明：N2和N11频谱值的分布带窄，低频重力场显著，中频重力场不显著；N9和N10的频谱值分布带宽，中频和低频重力场均显著。分析了它们和地质构造的关系。曾母盆地、南华盆地和南薇盆地的低频重力异常和沉积厚度成反关系，其余地区成正关系。     

南海表层水温甚低频振荡的动力学机制

用一个简单的海洋模式，研究了东亚季风异常对南海表层水温（ＳＳＴ）的影响，发现南海表层水温的甚低频振荡是东亚季风异常风应力强迫所致．这种甚低频振荡主要反映在深水区，其空间分布呈椭圆形，几乎与南海海盆形状一致。从海盆中央到边缘振幅逐渐减少，ＳＳＴ的甚低频振荡是非行进波，无明显传播特征。     

液舱三维晃荡运动二阶共振理论解及特性分析

从无旋运动的理论出发,并利用微扰法,推导了液舱三维晃荡运动二阶共振问题的理论解。考虑纵荡和横荡运动情况,对液舱三维晃荡二阶共振问题进行了分析。当两个晃荡方向的和频(即其外部激发频率的和)或差频(即其外部激发频率的差值)等于液舱固有频率时,二阶共振发生;当某一晃荡方向(横荡或纵荡)外部激发频率与另一晃荡方向(纵荡或横荡方向)液舱某一固有频率的和或差值等于液舱另一固有频率时,二阶共振也会发生。进一步研究了各个二阶共振激发频率下水深变化对晃荡振幅的影响。结果表明,对于两个晃荡方向外部激发频率的和频和单一晃荡方向(纵荡或横荡)某一个激发频率与另一晃荡方向(横荡或纵荡)某一个属于奇模的固有频率的和频所引发的共振情况,水深变化对共振振幅大小的影响比较大;而对于相应差频所引发的共振情况,水深变化对共振振幅大小的影响比较小。     

基于微结构图像的风生微尺度波频率谱初探

利用海面微结构光学测量装置实验获取到的微尺度波图像来给出风生微尺度波的波数谱,在此基础上利用频散关系建立微尺度波波数谱和频率谱之间的关系,最终得到微尺度波频率谱.对微尺度波的频率谱随频率变化的响应进行了研究,发现频率谱与频率的a次方成正比关系,a的值随风速的增加而增加,同一风速下a几乎为定值.     

不规则波下船舶运动响应特征数值分析

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。     

Numerical Study of Two-Dimensional Focusing Waves

Two-dimensional focusing waves are generated and investigated by numerical method. The numerical model is developed by introducing the wave maker boundary on the high-order spectral （HOS） method proposed by Dommermuth and Yue in 1987 and verified by theoretical and experimental data. Some cases of focusing waves considering different parameters such as assumed focusing amplitudes, frequency bandwidth, central frequency and frequency spectrum are generated. Characteristics of the focusing wave including surface elevations, the maximum crest, shift of focusing points and frequency spectra are discussed. The results show that the focusing wave characteristics are strongly affected by focusing amplitudes, frequency bandwidth, central frequency and frequency spectrum.     

Target localization and tracking from Doppler-shift measurements

It is possible to localize a nonmaneuvering moving source radiating a constant frequency tone from measurements of the Doppler-shifted frequency at several sensors. Due to the nonlinear nature of the problem, it is necessary to find the solution by grid searches. However, if measurements of the rates of frequency changes are available, the search is only in three dimensions instead of the normal five in source frequency, its x-y positions, and speeds. The validity of combining frequency and frequency-rate measurements is confirmed with simulation studies. The overall system includes a least-squares track-sort algorithm to differentiate the true track from the extraneous track, and a Kalman tracker for the prediction of future source positions, thereby reducing the grid search size. An error analysis relating localization accuracy to uncertainties in frequency measurements and sensor positions is also given     

支撑结构频率对海上风机动力响应的影响机理研究

海上支撑结构的优化设计是海上风机技术发展的必然趋势,降低支撑结构的载荷是保证风机安全运行的有效途径。海上支撑结构受到风浪复杂环境荷载作用,风、浪载荷决定着塔底承受较大的剪力和倾覆力矩,同时风浪的随机性和周期性会影响塔架的疲劳载荷。基于海上风机支撑结构频率对载荷影响的研究,分析海上支撑结构频率对叶片根部挥舞和摆振响应的影响,探究频率对风机响应的影响机理。研究表明：波浪频率诱导是基础疲劳载荷响应的主要原因;开展单桩基础设计,当整机频率确定时,基础变径段可设置于浪溅区下部区域范围;叶片摆振响应受1P频率影响较大,在风机设计时可增加叶片摆振方向的阻尼;当整机频率邻近3P频率时,塔筒刚度变化对基础载荷响应的影响大于基础刚度变化;海上支撑结构设计时可优先考虑塔筒刚度。     

Passive Doppler-bearing tracking using a pseudo-linear estimator

In this paper an explicit pseudo-linear estimator for Doppler-bearing tracking is proposed. It overcomes the problems with the bias of earlier pseudo-linear estimators and with the nonlinear frequency measurement equation by using another representation than the Cartesian one and by using the logarithm of the frequency, respectively. It is fast, inherently stable, and easy to implement. The Doppler shift is, for a nonmoving own-ship, determined by the target velocities, while the bearing rate is determined by the same velocities divided by the range. The special representation in this paper uses this difference in behavior to give fast and bias free estimation of the range. Instead of iterating a weighted feast squares problem using bearing and frequency measurements simultaneously, the true bearings and the course are estimated in a bearings only step followed by a frequency only step, which estimates range and frequency. The range estimate then gives the speed estimate. Modifications for scenarios with multiple emitted frequency lines and/or for frequency lines that disappear during parts of a scenario are shown     

由波浪压力记录计算表面波谱

对目前仍广为使用的压力测波仪来说,如何通过波浪在某深度处的压力信息来推算海面的波浪状况呢?根据深水小振幅简单波动的经典理论,关系式H_o=H_z exp[kz]成立,式中H_o、H_z分别表示海面和水深z处的波高。将这一关系式应用于实际资料,则由波浪压力记录可以求出H_z、T_z(或λ_z),再由记录的深度z就可以求出H_o。     

Dynamic Characteristics of Marine Risers Conveying Fluid

The lateral vibration differential equation for a marine riser conveying fluid is derived by useof the small deflection theory.and the effect of internal flow velocity and top tension on the natural fre-quency of the riser is studied by use of FEM.At the same time,the preliminary relationship between thenatural frequency and riser span under different internal flow velocities is obtained,the effect of riser sup-ports on the vibration frequency is computed.It is found that the natural frequency of the marine riser in-creases with the increase of top tension.however decreases with the increase of internal flow velocity.In ad-dition,the frequency decreases drastically with the increase of riser span.     

Analysis of Dynamic Characteristics of Submarine Free Spanning Pipelines by Complex Damping Method

Considering the effect of the internal flowing fluid and the external marine environmental condition, the differential equation for the vortex-induced vibration (V1V) of the free spanning pipeline is derived and is discretized by the Hermit interpolation function. The free vibration equation with the damping term is solved by the complex damping method for the natural frequency, and then the effect of fluid damping on the natural frequency of the free spanning pipeline is analyzed.The results show that fluid damping has a significant influence on the damped natural frequency of the free spanning pipeline in the lock-in state, while it has little influence when the pipeline is out of the lock-in state. In the meantime,the change of the free span length has the same effect on the damped natural frequency and the undamped natural frequency.     

风浪槽内风浪外频谱谱形的一些特征

利用实验室风浪槽内测得的波面序列资料估计风浪外频谱。通过与实测风浪内频谱的比较,研究实测风浪外频谱的谱形特征,探讨海浪外频谱与内频谱的相似性问题。此外,还检验一种理论海浪外频谱。     

Analysis of Energy Overshoot of High Frequency Waves with Wavelet Transform

—A study is made on the overshoot phenomena in wind-generated waves.The surface displace-ments of time-growing waves are measured at four fetches in a wind wave channel.The evolution of highfrequency waves is displayed with wavelet transform.The results are compared with Sutherland's. It isfound that high frequency wave components experience much stronger energy overshoot in the evolution.The energy of high frequency waves decreases greatly after overshoot.     

最平滤波器在分析月平均潮位资料中的应用

应用数字滤波方法来消除验潮资料中的高频扰动而分离出海平面的趋势性变化，并设计了最平滤波器；对其幅频响应特性和相位特性的验证表明，最平滤波器的技术性能基本上是可靠的。应用最平滤波器对月平均验潮序列进行低通数字滤波，可以有效地消除验潮资料中的高频扰动，分离出低频变化。从数值计算过程、高频扰动机制及实测验潮资料的估算结果来看，低通数字滤波在确定海平面长期变化趋势中，对消除高频扰动的影响是非常重要而有效的。     

基于DDS技术的噪声分析及抑噪实现

直接数字合成(DDS)是一种重要的频率合成技术,具有分辨率高、频率变换快等优点,在雷达、海洋ADCP及通信等领域有着广泛的应用前景。文中对DDS技术所含有的噪声进行了剖析,并得出结论,在量化字长一定的情况下,产生波形的频率误差与参考频率有很大的关系,参考频率越高,波形质量越好,并且当信号的当参考时钟频率与所发射波形频率之比小于10：1时,波形会产生明显的失真;针对DDs技术的噪声,结合具体的数字合成芯片AD9854,提出了一种设计Butterworth滤波器去噪的方法,该方法简单,易行,具有良好的通用性。     

水下悬浮隧道锚索稳定性分析

为研究水下悬浮隧道锚索的稳定性,建立锚索在涡街激励作用下振动的数学方程,采用伽辽金法对其进行化简,锚索振动的稳定性通过Lyapunov指数法进行判断,分析了锚索动静张力比的大小、悬浮隧道系统的阻尼比和锚索参数激励频率对锚索振动稳定性的影响。计算结果表明,锚索振动失稳的范围取决于锚索的动静张力比、锚索的阻尼比和频率比(锚索参数激励频率与锚索1阶模态固有频率的比值);当频率比为1和2左右时,随着锚索动静张力比的增大和阻尼比的减小,锚索逐渐从稳定状态转变为不稳定状态,且锚索的不稳定区域逐渐增大。     

近60年西北太平洋台风年代际变化特征及成因的初步分析

利用60年台风资料,对西北太平洋台风的频数、路径和强度变化做统计分析。结果表明:西北太平洋的台风活动在20世纪60年代是高峰期,70年代则是低谷期,从20世纪90年代后期开始,台风活动总体处于低谷期;台风路径主要以转向为主,在20世纪60、70年代平均路径比较偏南,而进入21世纪后平均路径比较偏北;强度在20世纪50、60年代总体较强,后25年总体较弱;西北太平洋台风异常偏多时,西北太平洋副高弱且位置偏东,太平洋海温分布呈"拉尼娜"特征;台风异常偏少时,副高强且位置偏西,太平洋海温分布呈"厄尔尼诺"特征。     

Processing irregular wave measurements to enhance point absorber power capture performance

The paper aims at introducing practical methods for power capture performance enhancement of a heaving wave energy converter in irregular seas. The optimum control solution requires tuning to wave frequency based on wave force information. However, identification of the wave frequency in irregular seas is considered to be a complex and difficult task. This is partly due to technical difficulties in determination of the wave force. Besides, there are no clear guidelines for identification of wave frequency from an irregular sea state based wave force information. In a typical application, one of the available sources of information about the wave properties is the wave elevation record. The proposed approach presents a method for estimation of the wave frequency information from the wave elevation data by using signal processing and filtering techniques. The proposed method uses filters to generate an estimation of wave force information, which is used to identify the local wave frequency by method of a time-series analysis of the data. This wave frequency information is then used in tuning the device. The details of the proposed techniques, the model of the wave energy converter, the simulated sea states and the related simulation results are also presented.     

Infragravity Waves Produced by Wave Groups on Beaches

The generation of low frequency waves by a single or double wave groups incident upon two plane beaches with the slope of 1/40 and 1/100 is investigated experimentally and numerically. A new type of wave maker signal is used to generate the groups, allowing the bound long wave (set-down) to be included in the group. The experiments show that the low frequency wave is generated during breaking and propagation to the shoreline of the wave group. This process of generation and propagation of low frequency waves is simulated numerically by solving the short-wave averaged mass and momentum conservation equations. The computed and measured results are in good agreement. The mechanism of generation of low frequency waves in the surf zone is examined and discussed.