大容量舱容积计量的快速测量新方法

针对不断大型化和多样化的船舶与海洋结构物舱室,为适应其舱容测量需求,借鉴传统的容量比较法和几何测量法,提出了一种新的高效、准确、适用性强的舱容测量方法。新测量方法采用间接积分计算舱容思路,包含实验与计算两个部分;实验中标准容器注水和未知体积大量注水交替进行,再将实验数据转化为可以描述舱容变化趋势的水线面积数据;计算部分基于水线面积数据、采用收敛性较好的样条插值方法得到近似水线面积曲线,并进一步积分得到测量舱容曲线。通过算例验证,相对于传统测量方法,该方法可以更方便、高效地完成大容量舱的容积测量,同时具有很高精度;并可根据舱体特点灵活安排测量方案,更好地解决测量效率与精度间的矛盾。     

An efficient algorithm for generating a spherical multiple-cell grid

This paper presents an efficient algorithm for generating a spherical multiple-cell(SMC) grid. The algorithm adopts a recursive loop structure and provides two refinement methods:(1) an arbitrary area refinement method and(2) a nearshore refinement method. Numerical experiments are carried out, and the results show that compared with the existing grid generation algorithm, this algorithm is more flexible and operable.     

An efficient algorithm for simulating the dynamics of towed cable systems

An efficient algorithm is presented which simulates the three-dimensional motion of a towed cable. The formulation is based on an implicit, second-order finite difference approximation of the equations of motion. The results of the computation are compared both to those obtained by another numerical model and to experimental measurements.     

An efficient shock capturing algorithm to the extended Boussinesq wave equations

A hybrid finite-volume and finite-difference method is proposed for numerically solving the two-dimensional (2D) extended Boussinesq equations. The governing equations are written in such a way that the convective flux is approximated using finite volume (FV) method while the remaining terms are discretized using finite difference (FD) method. Multi-stage (MUSTA) scheme, instead of commonly used HLL or Roe schemes, is adopted to evaluate the convective flux as it has the simplicity of centred scheme and accuracy of upwind scheme. The third order Runge–Kutta method is used for time marching. Wave breaking and wet–dry interface are also treated in the model. In addition to model validation, the emphasis is given to compare the merits and limitations of using MUSTA scheme and HLL scheme in the model. The analytical and experimental data available in the literature have been used for the assessment. Numerical tests demonstrate that the developed model has the advantages of stability preserving, shock-capturing and numerical efficiency when applied in the complex nearshore region. Compared with that using HLL scheme, the proposed model has comparable numerical accuracy, but requires slightly less computation time and is much simpler to code.     

基于不规则矩形划分的高效海洋环流数值模式并行算法

使用序列化和不规则矩形划分的方法,开发了基于消息传递接口(MPI)的环流数值模式并行算法,并通过邻近点交换策略(NPES)进一步提升了计算效率。在HP C7000刀片系统上设计了两个实验,数值结果表明,使用了NPES的并行版本(PVN)的计算效率要高于原并行版本(PV)。在第二个实验中当进程数为100时PVN的计算效率仍可达到0.9以上,然而此时PV的计算效率已迅速下降至0.39。并用环流模式的PVN版本对一个高分辨率的区域进行了模拟,效果较好。该算法具备普适性,可用于其它环流模式的高效并行。     

Ship motion measurement filter design

A procedure is presented for designing Kalman filters to measure linear and angular ship motion parameters using realistic models of the ship motion dynamics. The design is based on the state space modeling of ship motion dynamics. The designed filters exhibited significant accuracy improvement (order of magnitude) over filters which do not model ship dynamics. The sensitivity of the filter mechanization to mismodeling of dynamics is investigated. Bounding filter design techniques are used to minimize the effects of mismodeling. The particular measurement system investigated consisted of linear and angular accelerometers in a strapdown mode. The design techniques are also applicable to inertial instruments in a stable inertial platform mode.     

An efficient architecture for real-time narrowband beamforming

A short finite impulse response (FIR) filter architecture for narrowband beamforming is presented that is well suited for active sonar applications. By applying the technique of adaptive modeling, a short FIR filter can be designed to carry out any required narrowband constant phase shift. A 4-tap FIR filter designed in this way can generate constant phase shift within bandwidths of 0.04 (relative to the sampling frequency), with an error of less than 1°. Thus a beam can be formed with a bank of short FIR filters, each filter corresponding to one sensor. Due to the light computational load of this method, it is rather convenient for digital signal processors (DSP) to implement beamforming in real time. Satisfactory sonar beam patterns are shown to result from a TMS320C25-based emulation of the architecture     

An efficient approach for characterizing basin-scale hydrodynamics

As the upstream oil and gas sector continues to use more groundwater resources for their operations, a comprehensive understanding of formation fluids at the sedimentary basin scale is required to inventory and manage available groundwater resources. Basin-scale fluid flow is often simplified to only assess pre-development groundwater conditions without understanding how large-scale hydrocarbon development might be changing regional flow patterns. This study focuses on two aspects of hydrogeological mapping for characterizing basin-scale hydrodynamics: (1) assessing the influence of hydrocarbon production and injection on pressure measurements used to map hydraulic heads and infer groundwater conditions; and (2) determining the effects of variable density groundwater on understanding the magnitude and direction of flow primarily in saline formation water aquifers. Drillstem Tests (DST's) are transient pressure tests that are used to infer regional groundwater flow, but they can be strongly affected when the sample location is located within the vicinity of a hydrocarbon production or injection well. To identify production and injection influences this study implements a Cumulative Interference Index (CII) methodology. This implementation can be used to map pre-development groundwater flow conditions and evaluate regional changes or effects due to historical oil and gas activity. Density effects are often neglected and can have considerable effect on groundwater flow in cases where aquifers contain dense brines, are inclined and sloping, or possess weaker hydraulic gradients than the buoyancy force potential. This study implements a vectorial analysis to identify flow directions in regions where density driven flow is important and can change the inferred magnitude and direction of flow. Two case studies are presented to demonstrate the effectiveness of these methodologies at evaluating basin-scale hydrodynamics.     

An adaptive-hybrid algorithm for geoacoustic inversion

This paper presents an adaptive hybrid algorithm to invert ocean acoustic field measurements for seabed geoacoustic parameters. The inversion combines a global search (simulated annealing) and a local method (downhill simplex), employing an adaptive approach to control the trade off between random variation and gradient-based information in the inversion. The result is an efficient and effective algorithm that successfully navigates challenging parameter spaces including large numbers of local minima, strongly correlated parameters, and a wide range of parameter sensitivities. The algorithm is applied to a set of benchmark test cases, which includes inversion of simulated measurements with and without noise, and cases where the model parameterization is known and where the parameterization most be determined as part of the inversion. For accurate data, the adaptive inversion often produces a model with a Bartlett mismatch lower than the numerical error of the propagation model used to compute the replica fields. For noisy synthetic data, the inversion produces a model with a mismatch that is lower than that for the true parameters. Comparison with previous inversions indicates that the adaptive hybrid method provides the best results to date for the benchmark cases     

An efficient focusing model for generation of freak waves

Based on the Longuet-Higgins wave model theory, the previews studies have shown that freak waves can be generated in finite space and time successfully. However, as to generating high nonlinear freak waves, the simulation results will be unrealistic. Therefore, a modified phase modulation method for simulating high nonlinear freak waves was developed. The surface elevations of some wave components at certain time and place are positive by modulating the corresponding random initial phases, then the total surface elevation at the focused point is enhanced and furthermore a freak wave event is generated. The new method can not only make the freak wave occur at certain time and place, but also make the simulated wave surface time series satisfy statistical properties of the realistic sea state and keep identical with the target wave spectrum. This numerical approach is of good precision and high efficiency by the comparisons of the simulated freak waves and the recorded freak waves.     

An efficient retrospective optimal interpolation algorithm compared with the fixed-lag Kalman smoother by assuming a perfect model

We developed an efficient retrospective optimal interpolation (ROI) algorithm by which we can avoid the overlap of model integration periods, which appears in the procedure of evolving a previous analysis error covariance. If the fixed-lag Kalman smoother (FLKS) is used to determine the analysis state at the beginning of the fixed analysis window as is done for ROI, the FLKS can be considered a suboptimal version of the efficient ROI when the involved model is non-linear and has no errors. We confirm that the efficient ROI analyses are more accurate than the FLKS analyses with the increase of the analysis window size. Nevertheless, the computation costs for implementing efficient ROI are almost the same as those for FLKS. Additionally, the reduced-rank version of the efficient ROI is developed based on the accuracy-saturation property.
From the experiments using Lorenz 3-variable model, it is confirmed that the non-linearity of numerical model, which becomes stronger with the increase of the analysis window size, makes the analysis of efficient ROI more accurate than that of FLKS. Our Lorenz 40-variable experiments show that the average analysis error of the efficient ROI is smaller than that of the FLKS for an analysis window size of up to 4 d. However, the efficient ROI and the FLKS requires almost the same costs for computation. From the results of Lorenz 40-variable model experiments, it is suggested that, by using the reduced-rank formulation of the efficient ROI, we can obtain the suboptimal analysis more cost-effectively rather than FLKS.     

An efficient mode-splitting method for a curvilinear nearshore circulation model

A mode-splitting method is applied to the quasi-3D nearshore circulation equations in generalized curvilinear coordinates. The gravity wave mode and the vorticity wave mode of the equations are derived using the two-step projection method. Using an implicit algorithm for the gravity mode and an explicit algorithm for the vorticity mode, we combine the two modes to derive a mixed difference–differential equation with respect to surface elevation. McKee et al.'s [McKee, S., Wall, D.P., and Wilson, S.K., 1996. An alternating direction implicit scheme for parabolic equations with mixed derivative and convective terms. J. Comput. Phys., 126, 64–76.] ADI scheme is then used to solve the parabolic-type equation in dealing with the mixed derivative and convective terms from the curvilinear coordinate transformation. Good convergence rates are found in two typical cases which represent respectively the motions dominated by the gravity mode and the vorticity mode. Time step limitations imposed by the vorticity convective Courant number in vorticity-mode-dominant cases are discussed. Model efficiency and accuracy are verified in model application to tidal current simulations in San Francisco Bight.     

椭圆型缓坡方程的一个有效的有限元解

将海绵层消波的方法用于有限元方法中,提出了缓坡方程的一种有效的有限元求解方法.在应用有限元法求解椭圆型缓坡方程时,通过在方程中加摩阻项,并在入射边界(波浪由此边界进入计算域)处使用不连续单元,将绕射势从总势中分离出来,在边界上利用海绵层进行消波处理,有效地消除了由于引用放射边界条件引起的误差和数值反射现象.     

声学法深海热液速度场测量重建算法研究

介绍了利用声学法测量深海热液速度场的基本原理.利用往返飞渡时间差与流场速度的关系,应用反问题求解技术重建测量区域的速度场.应用最小二乘法对两种典型的热液口速度场模型进行了仿真重建,分析了换能器数量、实验测量误差以及换能器的布放对重建结果的影响,并对重建结果进行了流量分析.仿真重建的绝对误差、相对误差以及流量分析结果表明...     

A new Doppler frequency anomaly algorithm for surface current measurement with SAR

Values for Doppler center frequency are calculated from the echo signal at the satellite using the Doppler centroid method and so include the predicted Doppler ...     

An analysis of mechanisms for submesoscale vertical motion at ocean fronts

We analyze model simulations of a wind-forced upper ocean front to understand the generation of near-surface submesoscale, O(1 km), structures with intense vertical motion. The largest vertical velocities are in the downward direction; their maxima are situated at approximately 25 m depth and magnitudes exceed 1 mm/s or 100 m/day. They are correlated with high rates of lateral strain, large relative vorticity and the loss of geostrophic balance. We examine several mechanisms for the formation of submesoscale structure and vertical velocity in the upper ocean. These include: (i) frontogenesis, (ii) frictional effects at fronts, (iii) mixed layer instabilities, (iv) ageostrophic anticyclonic instability, and (v) nonlinear Ekman effects. We assess the role of these mechanisms in generating vertical motion within the nonlinear, three-dimensionally evolving flow field of the nonhydrostatic model. We find that the strong submesoscale down-welling in the model is explained by nonlinear Ekman pumping and is also consistent with the potential vorticity arguments that analogize down-front winds to buoyancy-forcing. Conditions also support the formation of ageostrophic anticyclonic instabilities, but the contribution of these is difficult to assess because the decomposition of the flow into balanced and unbalanced components via semigeostrophic analysis breaks down at O(1) Rossby numbers. Mixed layer instabilities do not dominate the structure, but shear and frontogenesis contribute to the relative vorticity and strain fields that generate ageostrophy.     

An efficient solver for nearshore flows based on the WAF method

We describe an efficient and robust flow solver for the integration of the classic Nonlinear Shallow Water Equations (NSWE) on a beach of arbitrary topography. On the basis of the ‘shock capturing’ Weighted Average Flux (WAF) method, a numerical code is implemented which employs a space-splitting technique to integrate the NSWE over a horizontally two-dimensional domain (2DH). Special care is put in handling the moving shoreline and a new, efficient formulation of the shoreline boundary conditions is presented. This is based on the hydrodynamic equivalent of the cavitation condition used in gas dynamics. Model capabilities are illustrated by means of a number of tests (both 1DH and 2DH). These reveal that, though primarily conceived for modelling nearshore hydrodynamics, the solver can be successfully adopted even for studying the run-up of large tsunami waves.     

基于二元LSTM神经网络的船舶运动预测算法研究

在海况环境下,进行船舶运动预测时.由于惯性传感器采集系统本身的电学特性,会产生误差偏移,影响预测的准确性.针对这一问题,在常规长短期记忆网络(LSTM)的基础上,设计改良了一种二元的LSTM网络架构.在船舶运动仿真平台上进行模拟船舶升沉运动实验,并通过惯性传感系统测量仿真平台实时积分位移进行计算验证.验证统计该网络预测...     

A fast algorithm for high-accuracy frequency measurement:application to ultrasonic Doppler sonar

In an attempt to investigate the technical feasibility of a CW Doppler sonar, we have examined a method of measuring low velocities with a high-velocity resolution, or frequency resolution, by use of a simple circuit configuration employing digital signal processing technique. The following discussion presents the results of the investigation. In the measuring method described, the fast Fourier transform (FFT) of undersampled data is calculated and the Doppler shift is obtained by searching for a peak frequency of the power spectrum. To achieve the intended frequency resolution of 1 Hz by FFT operation, measurement of data for a minimum measuring period of 1 s is essential. If the sampling frequency is set to 50 kHz, the number of samples obtained during the minimum measuring period of I s would amount to 50000. This is not practical in light of the time required for the FFT operation. To overcome this problem, our new measuring method employs a decimation technique for reducing the number of samples down to 1024 while maintaining a frequency resolution of about 1 Hz. This paper describes how the processing time can be drastically reduced to about 1/300th compared to the conventional technique by a combination of complex exponential functions, filtering and decimation, and thereby indicates the possibility of real-time CW Doppler data processing