A novel array of elliptic ring radiators

An array of elliptic ring radiators is proposed which generates a fan-type beam with controllable sidelobe levels. Such an array has applications in specialized acoustic systems such as sidescan sonars, sonars for fish finding and stock assessment, obstacle avoidance systems, and others. Two possible approaches to the design are presented. One approach utilizes a mapping which transforms a radiation pattern generated by a circular ring array to that of an elliptic ring array. This approach takes advantage of methodologies developed for the design of circular ring arrays. The other approach uses the concept of an equivalent linear array. This approach benefits from existing design techniques developed for linear arrays. It requires only simple matrix operations and does not involve any optimization. The design examples presented demonstrate that a fan-type beam with sidelobes suppressed to more than 40 dB in all possible directions is achievable     

A novel array of ring radiators

An array of ring radiators which generates a symmetric search-light-type narrow beam with greatly reduced sidelobes is proposed. Such a narrow beam can find several applications related to acoustic remote sensing, telemetry, and specialized sonars. A design procedure which benefits from design techniques developed for linear arrays is detailed. The developed methodology requires only simple matrix operation and does not involve nonlinear optimization. The results indicate that radiation patterns with arbitrary sidelobe suppression can be achieved     

An iterative method for array pattern synthesis

The authors propose a novel iterative method for synthesizing radiation patterns of linear arrays with arbitrary sidelobe envelopes, with nonisotropic elements, and with nonuniform spacing between elements. Various design examples are presented and compared with other methods. It is shown that the proposed iterative method converges rapidly and yields superior results over other methods     

Self-monitoring sonar transducer array with internal accelerometers

To achieve the maximum detection range for active sonars, it is desirable to maximize their acoustic power. In attempting to do so, there are two limitations which are caused by cavitation on the face of the transducer and an interaction effect between transducer elements of the array. To avoid these limitations, a method is proposed for driving the array elements in phase with a uniform velocity to yield the desired radiation. For this purpose, a sonar transducer array which has internal accelerometers for monitoring the motion of the transducer element is being developed. This paper presents an outline of this sonar array and a method of high-speed numerical calculation which was developed for the prediction of the radiation characteristics of the array using the fractional Fourier transform algorithm     

Temporal domain processing for a synthetic aperture array

A method for the synthesis of an aperture with improved bearing resolution and signal gain is described. The proposed method temporally synthesizes data from an overlap correlator, which is obtained by aperture domain averaging of phase differences. Previous studies, such as extended towed array measurements (ETAM), had a restriction in that the overlapped hydrophones between successive measurements of a towed array were required to have identical positions in space. In this paper, however, it is shown that the phase correction factors can be estimated without restriction on the positions of the overlapped hydrophones. This implies that the proposed method is able to utilize more snapshots to extend the towed array. Simulation results showed that the proposed method resulted in higher estimation accuracy than ETAM. In addition, the effects of coherency and other systematic errors on the proposed method were examined     

Mooring optimization of floating platforms using a genetic algorithm

This paper presents a new procedure for the optimization of the mooring design of floating platforms, in which an automatic design sequence is also established. Regarding the optimization philosophy, the following aspects are dealt with:

• The optimization of the platform heading and its mooring pattern, taking into account the environmental force spreading;

• optimum line length or line tension for each mooring line, associated to the optimization of the mooring line materials and sizes.

Basically, the main goal of this paper is to introduce a new method, which will provide the quickest way to find the best mooring system, defined here as that which minimizes platform responses.A genetic algorithm (GA) is applied in this contribution, and this paper describes exactly the procedure of developing a GA code directed toward the solution of mooring design optimization problems. In order to prove the efficiency and the vast potential of the proposed algorithm as a design tool, sample moorings are analyzed for different environmental conditions and the final results, including the time required to run them, are presented.     

基于全局性极小化二维反投影误差的射影重建方法

建立1种新的射影重建方法。该方法以全局性极小化射影三维空间点的二维反投影误差平方和为准则,相对于缩小SVD反投影误差的方法,具有更为明确合理的物理意义。实现过程是以奇异值分解为基本工具的分步线性迭代计算,避免了传统射影重建方法复杂的非线性优化环节。它无需估计投影深度,避免了基础矩阵计算的复杂性问题,因而也不受相机特殊运动的限制。文中利用虚拟物体图像和真实物体图像进行了实验验证,证明该方法具有计算简单、准确性和鲁棒性高等方面的特点,具有较高的实用价值。     

船舶管线隔振支座布局几何优化设计方法

海洋工程船舶管线隔振支座布局直接影响到管线整体的结构性能和经济性。在船舶管线隔振支座布局优化规范设计法的基础上,进一步提出了隔振支座布局几何优化设计模型与方法。该方法假定支座总数目,采用迭代优化算法求解,通过确定各支座的几何位置坐标实现布局优化。该迭代算法依据约束条件的满足情况及变步长的临界间距值来确定支座数量的减少与增加,最终得到较优的支座数目及间距。以应用于某舰艇的二维管道为例,用该方法对其隔振支座布局进行优化设计,并将不同目标函数下的优化结果同规范设计法所得结果进行了对比。比较结果表明,该模型与方法具有较好的可行性与稳定性。     

Adaptive beamforming of a towed array during a turn

During maneuvering, towed array beamforming degrades if a straight array is assumed. This is especially true for high-resolution adaptive beamforming. It is experimentally demonstrated that adaptive beamforming is feasible on a turning array, provided that array shape is estimated. The array shape can be inferred solely from the coordinates of the tow vessel's Global Positioning System (GPS) without any instrumentation in the array. Based on estimated array shape from the GPS, both the conventional beamformer and the white noise constrained (WNC) adaptive beamformer are shown to track the source well during a turn. When calculating the weight vector in the WNC approach, a matrix inversion of the cross-spectral density matrix is involved. This matrix inversion can be stabilized by averaging the cross-spectral density matrix over neighboring frequencies. The proposed algorithms have been tested on real data with the tow-vessel making 45/spl deg/ turns with a 500-m curvature radius. While turning, the improvement in performance over the assumption of a straight array geometry was up to 5 dB for the conventional beamformer and considerably larger for the WNC adaptive beamformer.     

A new methodology developed by cetena to assess the seakeeping behaviour of marine vessels

The paper describes an analytical method to determine an operability index for a marine vehicle when its geometric characteristics, the geographical area in which the vessel is supposed to operate, and the limiting criteria for operations are known. The computer program based on strip theory provides reliable results not only for conventional hullforms, but also for catamarans, offshore vehicles, etc. The results are presented in the form of figures for different vessels, namely, crane barge, naval vessels and SWATH type catamarans. The authors are of the opinion that the proposed method would provide the designer with a valid tool to improve the seakeeping qualities of a vessel, while taking into account the limiting conditions imposed due to seaway operations.     

极化SAR目标相对最优极化研究

目标相对最优极化就是选取一种极化状态,使得研究目标和背景地物的接收功率对比达到最大。通过讨论了目标相对最优极化问题,提出了改进的模型和解算方法,利用实际数据对其模型和方法进行了实验,验证了其有效性和正确性。     

THE COMPUTATION OF OPTIMUM OCEAN SHIP ROUTING

A computational method for the ocean ship routing based on optimization theory is presented in this paper. In the computational programme "breaking circle method" is used, by which a principal contradictory line can be obtained in the operations research. The automatic selection of calculating network and the initial values have been realized. The quantitative estimation for the change of navigating speed under the different conditions of ocean wave and current has been done. The objectivly quantitative computational method is provided for ocean ship routing and forecast service following ship tracks. The calculating examples and practical experiments of ships have proved that this computational method is highly effective.     

Optimization Design of Fairings for VIV Suppression Based on Data-Driven Models and Genetic Algorithm

Vortex induced vibration(VIV)is a challenge in ocean engineering.Several devices including fairings have been designed to suppress VIV.However,how to optimize the design of suppression devices is still a problem to be solved.In this paper,an optimization design methodology is presented based on data-driven models and genetic algorithm(GA).Data-driven models are introduced to substitute complex physics-based equations.GA is used to rapidly search for the optimal suppression device from all possible solutions.Taking fairings as example,VIV response database for different fairings is established based on parameterized models in which model sections of fairings are controlled by several control points and Bezier curves.Then a data-driven model,which can predict the VIV response of fairings with different sections accurately and efficiently,is trained through BP neural network.Finally,a comprehensive optimization method and process is proposed based on GA and the data-driven model.The proposed method is demonstrated by its application to a case.It turns out that the proposed method can perform the optimization design of fairings effectively.VIV can be reduced obviously through the optimization design.     

Numerical study on attenuation of bubble pulse through tuning the air-gun array with the particle swarm optimization method

A numerical method for improving the quality of the far-field signal generated by a marine seismic air-gun array is presented, in which particle swarm optimization is used in conjunction with the theory of the oscillating spherical bubble to tune the array. Two sets of objective functions, including the primary-to-bubble ratio and the variance of the normalized amplitude spectrum, are built to screen the array. With this method, attempts are made to improve the far-field signals generated by four typical arrays, including the planar array, spatial array, irregular array and delayed array. It is concluded that the far-field signal can be largely improved just through the simple adjustment of the chamber volume, the firing depth, the horizontal location or the firing time of each individual gun in the array. We believe that this method will be useful in the air-gun array design and helpful to find a desirable array from a population of air-gun array distributions for a brief time.     

Accurate measurement of six Degree Of Freedom small-scale ship motion through analysis of one camera images

A new six Degree Of Freedom (6DOF) motion measurement technique for small-scale physical models of floating bodies is presented, based on analysis of image sequence from one camera. The proposed system consists of one camera and one target: the method estimates the 3-D rigid motion following the time evolution of the target of known pattern fixed to the moving body and framed by the camera. In particular, the rotation matrix and the translation vector of the 3-D rigid motion between initial still position and a generic moved position are calculated by assuming the existence of a planar homography between the camera CCD plane and the plane passing through the flat target surface. Geometrical relationship allows one the calculation of wanted 6DOFs for every point of the modeled body. In the paper, the method is mathematically presented in terms of equations of rigid motion with its associate accuracies. The image-based technique is illustrated on some tests carried out in an experimental multipurpose wave basin.     

Extraction of ocean wave parameters from HF backscatter received bya four-element array: analysis and application

An algorithm that would extend the capabilities of a four-element square array known as the Coastal Oceans Dynamics Applications Radar (CODAR) to include the yielding of directional wave-height spectra from backscattered radiation is addressed. General expressions for the first- and second-order broadbeam radar cross-sections of the ocean surface are applied to the array. A Fourier-basis-function approach allows the broadbeam cross-sections to be written as a system of integral equations. The second-order radar return involves a double integral whose integrand contains nonlinear combinations of the unknowns, namely, the Fourier coefficients of the ocean wave directional spectrum. The first-order portion of the radar spectrum is used to linearize this integral. The matrix system then formulated is solved using a singular value decomposition (SVD) approach, and the resulting ocean spectral coefficients are used to give the directional spectrum. Test results for the algorithm are reported and discussed     

Hydrodynamic interference between floating cylinders in oblique seas

The hydrodynamic interference phenomena arising from multiple two-dimensional horizontal cylinders interacting with obliquely incident linear monochromatic waves are treated. A finite element method incorporating radiation boundary dampers is employed to solve the corresponding diffraction/radiation boundary value problems, where flexural mode responses are assumed. Both extreme cases of a rigidly connected catamaran and freely floating cylinders are studied in detail. Numerical results of both cases compare closely with those obtained by the method of multipoles. Important interference phenomena are identified which would assist in the design of facilities and operations involving multiple structures.     

Interaction of linear waves with an array of infinitely long horizontal circular cylinders in a two-layer fluid of infinite depth

The linear water wave scattering and radiation by an array of infinitely long horizontal circular cylinders in a two-layer fluid of infinite depth is investigated by use of the multipole expansion method. The diffracted and radiated potentials are expressed as a linear combination of infinite multipoles placed at the centre of each cylinder with unknown coefficients to be determined by the cylinder boundary conditions. Analytical expressions for wave forces, hydrodynamic coefficients, reflection and transmission coefficients and energies are derived. Comparisons are made between the present analytical results and those obtained by the boundary element method, and some examples are presented to illustrate the hydrodynamic behavior of multiple horizontal circular cylinders in a two-layer fluid. It is found that for two submerged circular cylinders the influence of the fluid density ratio on internal-mode wave forces is more appreciable than surface-mode wave forces, and the periodic oscillations of hydrodynamic results occur with the increase of the distance between two cylinders; for four submerged circular cylinders the influence of adding two cylinders on the wave forces of the former cylinders is small in low and high wave frequencies, but the influence is appreciable in intermediate wave frequencies.     

Surface projections of array beam patterns

Described is an application of surface projection calculations of array beam patterns. An example is presented showing how the surface patch illuminated by the transmitted pulse from a monostatic active sonar system intersects the surface projection of the beam pattern as a function of time.     

Stochastic optimization of linear sparse arrays

In conventional beamforming systems, the use of aperiodic arrays is a powerful way to obtain high resolution employing few elements and avoiding the presence of grating lobes. The optimized design of such arrays is a required task in order to control the side-lobe level and distribution. In this paper, an optimization method aimed at designing aperiodic linear sparse arrays with great flexibility is proposed. Simulated annealing, which is a stochastic optimization methodology, has been utilized to synthesize the positions and the weight coefficients of the elements of a linear array in order to minimize the peak of the sidelobes and to obtain a beam pattern that meets given requirements. An important novelty is the fact that the latter goal can be achieved in parallel to the minimization of both the number of elements and the spatial aperture, resulting in a “global” optimization of the array characteristics. The great freedom that simulated annealing allows in defining the energy function to be minimized is the main reason for the notable versatility and the good results of the proposed method. Such results show an improvement in the array characteristics and performances over those reported in the literature