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1.
The problem of propagation of obliquely incident surface water waves over a pair of asymmetrical rectangular trenches in a channel of finite depth is examined for its solution. The mathematical problem is handled for its numerical solution with the aid of a system of singular integral equations of first kind. The resulting integral equations are solved numerically by using suitably designed polynomial approximations of the unknown functions. System of linear algebraic equations is obtained by utilizing the zeros of Chebyshev polynomial of first kind as collocation points and hence the occurrence of ill-conditioned matrix is avoided. The effectiveness of the pair of trenches is studied by analyzing the physical quantities namely the reflection and transmission coefficients. As a special limiting case, the results for a single trench problem are derived and are found to be in excellent agreement with the results available in the literature. The effect of various parameters are analyzed through different graphs for a pair of asymmetrical trenches. The energy balance relation is derived and used to check the accuracy of numerical results. 相似文献
2.
浮托安装法,是相对于传统吊装法的一种新型海洋平台安装方法,具有起重能力大、作业周期短、安装费用低、适用范围广、操作安全方便等优点,解决了海上大型平台组块的安装问题。为了研究横荡护舷对浮托安装的影响,首先对海洋平台浮托安装中的护舷装置进行了介绍,然后针对某工程实例应用AQWA软件进行了数值模拟,并进行了模型验证。从时域方面对就位状态下的浮托模型进行了耦合动力分析,研究了横荡护舷参数对驳船运动和撞击力的影响规律。研究表明,横荡护舷可以有效地减小驳船运动和撞击力,其限位和缓冲作用与护舷尺寸及护舷刚度均有关。研究结果可为实际浮托安装工程提供重要的参考。 相似文献
3.
A new algorithm for automatic processing of bathymetric data 总被引：3，自引：0，他引：3
A sea-floor map can be obtained from sonar data using the supplied sonar system software or one of several public domain or proprietary systems. With any of these solutions, the process of production of a sea-floor map is unnecessarily time consuming in the absence of a systematic and efficient solution to the problem of identification of erroneous data (outliers). We present an algorithm to fit bathymetric data and to automatically deal with outliers. The most important characteristics of the algorithm are: production of a triangulated map in which the local spatial resolution and the local known accuracy are dependent both on the sea-floor topography and the data noise amplitude, automatic identification of outliers, intrinsic modularity of the program suitable for a multiprocessor environment, low computing cost, and minimal operator intervention. The algorithm is described and its parameters are defined on the basis of their effect on the results. The results of the application of the algorithm to synthetic data with and without outliers demonstrate its behavior on a known "sea floor". The results of the algorithm on real data and its performances (in term of speed and fitting error) are also tested. 相似文献
4.
The hydrodynamic problem of collision of an axisymmetric water block and solid boundary has been analyzed based on the velocity potential theory. The three dimensional axisymmetric hydrodynamic problem is converted to a quasi two dimensional one and is solved in axisymmetric coordinate system using the boundary element method. Numerical simulations are made for collision of a solid cone with a liquid cone or a spheroidal liquid block. The results in the former are compared with those obtained from similarity solution and excellent agreement is found. Numerical results are then presented for the collision between different solid cones and various spheroidal liquid blocks. 相似文献
5.
AbstractIn long baseline (LBL) positioning system, errors due to uncertain sound speed are the major facts to its positioning accuracy. In this study, the problem is solved by setting acoustic signal travels between the target and different hydrophones with different sound speed and using particle swarm optimization algorithm to solve the multi-parameter optimization problem to obtain the sound speeds. Presented simulation results show that the proposed algorithm can effectively improve the positioning accuracy of the LBL system compared to existing algorithms and its computational efficiency is high enough. 相似文献
6.
In this paper, a hybrid scheme based on a set of 2DH extended Boussinesq equations for slowly varying bathymetries is introduced. The numerical code combines the finite volume technique, applied to solve the advective part of the equations, with the finite difference method, used to discretize dispersive and source terms. Time integration is performed using the fourth-order Adams–Bashforth–Moulton predictor–corrector method; the Riemann problem is solved employing an approximate HLL solver, a fourth-order MUSCL-TVD technique is applied. Five test cases, for non-breaking and breaking waves, are reproduced to verify the model comparing its results to laboratory data or analytical solutions. 相似文献
7.
ROV accurate path following is challenging due to system unmodeled dynamics, disturbances and navigation sensors error. The model uncertainty and disturbances are commonly treated using robust methods such as the sliding mode controller where by incorporating an integral action in the zero tracking error is also guaranteed. Practically, the ROV position data is often computed using low cost inertial measurement unit (IMU) with outputs contaminated with bias and noise. Failure of mission is an immediate consequence of employing such biased sensors. However, the problem can be circumvented using the concept of redundant measurements and data fusion. In this respect, a set of 12 measurements from IMU, magnetometer and Doppler velocity log (DVL) are employed where the last two are aided sensors. The set up is shown to be capable of providing ROV path following with zero (in average) steady state tracking error irrespective of its dynamic parameters, environmental disturbances and erroneous data; as if it enjoys the exact values of the position of the ROV. It means that the combined DVL and magnetometer are sufficient for filtering the IMU biased measurements. Various simulations conducted confirm the results. 相似文献
8.
The performance of both the Capon and the MUSIC high resolution bearing estimation algorithms is investigated using both simulated data and sea test data collected with an experimental planar array. The major problem with these estimators is their sensitivity to both system errors and deviations from the assumed noise model. To alleviate this problem, two methods for preprocessing the data before they are input into the high-resolution algorithm are investigated: beam space and sector focused stability. The performance of both high-resolution estimators is examined, using both types of preprocessing, and the results are compared with those for the standard element-space (ES) techniques, assuming both finite cross-spectral-matrix (CSM) averaging errors and weakening target strengths. For the Capon estimator the performance is only superior to the standard element space technique when the CSM is calculated using a small number of averages. For the MUSIC estimator, both preprocessing techniques give clearly superior results over standard space techniques, with the SFS preprocessor performing the best 相似文献
9.
The design of mooring systems for floating production units usually considers extreme environmental conditions as a primary design parameter. However, in the case of FPSO (Floating, Production, Storage and Offloading) units, the worst response for the mooring system may be associated with other sea state conditions due to the fact that its extreme response may be associated with a resonant period instead of an extreme wave height. The best way to deal with this problem is by performing long-term analysis in order to obtain extreme response estimates. This procedure is computationally very demanding, since many short-term environmental conditions, and their associated stochastic nonlinear time domain numerical simulations of the mooring lines, are required to obtain such estimates. A simplified approach for the long-term analysis is the environmental contour-line design approach. In this paper a Monte Carlo-based integration procedure combined with an interpolation scheme to obtain the parameters of the short-term response distribution is employed to hasten the long-term analysis. Numerical simulations are carried out for an FPSO at three different locations considering a North Sea joint probability distribution for the environmental parameters. The long-term analysis results are compared against those obtained using extreme environmental conditions and environmental contour-line methodology. These results represent the characteristic load effect for the design of mooring systems of floating units using the reliability analysis for mooring line. The results show that the long-term results are usually more critical than those obtained with the other approaches and even different mooring lines can be identified as the critical ones. 相似文献
10.
In this paper the parameterizational approach of nonlinear source function and the implicit scheme of the model are discussed in detail. The matching problem is solved between time and space steps using the characteristics inlaid scheme with very strong physical meaning. The computational comparison in typical winds shows some improvements to the WAM model. That the hindcast results of the model for typhoon cases are in good agreement with real data illustrates its applicability to wave forecast and engineering study. 相似文献
11.
Numerical solutions for the hydroelastic problems of bodies are studied directly in the time domain using Neumann–Kelvin formulation. In the hydrodynamic part of problem, the exact initial boundary value problem is linearized using the free stream as a basis flow, replaced by the boundary integral equation applying Green theorem over the transient free surface Green function. The resultant boundary integral equation is discretized using quadrilateral elements over which the value of the potential is assumed to be constant and solved using the trapezoidal rule to integrate the memory or convolution part in time. In the structure part of the problem, the finite element method is used to solve the hydroelastic problem. The Mindlin plate as a bending element, which includes transverse shear effect and rotary inertia effect are used. The present numerical results show acceptable agreement with experimental, analytical, and other published numerical results. 相似文献
12.
The three-dimensional (3-D) eddy-current transient field problem is formulated first using theu-v method. This method breaks the vector Helmholtz equation into two scalar Helmholtz equations. Null-field integral equations and the appropriate boundary conditions germane to the problem are used to set up an identification matrix which is independent of null-field point locations. Embedded in the identification matrix are the unknown eigenvalues of the problem representing its impulse response in time. These eigenvalues are found by equating the determinant of the identification matrix to zero. The eigenvalues, which can be equated with temporal response, are found to be intimately linked to the initial forcing function which triggers the transient in question. When this initial forcing function is Fourier decomposed into its respective spatial harmonics, it is possible to associate with each Fourier component a unique eigenvalue by this technique. The true transient solution comes through a convolution of the impulse response so obtained with the particular imposed external field governing the problem at hand. The technique is applied to the FELIX medium cylinder (a conducting cylinder placed in a collapsing external field) and compared to data. A pseudoanalytic confirmation of the eigenvalues so obtained is formulated to validate the procedure. The technique proposed is applied in the low-frequency regime where the near-field effects must be considered. Application of the technique to a high frequency follows directly if the Coulomb gauge is adopted to represent the vector potential. 相似文献
13.
研究了时滞广义时变系统的渐近稳定和镇定问题。首先利用相关不等式,通过建立Lyapunov方程,给出了1个时滞广义时变系统无脉冲、渐近稳定性的充分条件。然后,基于这一工作,利用Riccati方程,进一步研究了时滞广义时变系统的镇定问题。最后,举例说明该结论的可行性。 相似文献
14.
《Oceanic Engineering, IEEE Journal of》2006,31(2):299-307
A common problem in sonar system prediction is that the ocean environment is not well known. Utilizing probabilistic based results from geoacoustic inversions we characterize parameters relevant to sonar performance. This paper describes the estimation of transmission loss and its statistical properties based on posterior parameter probabilities obtained from inversion of ocean acoustic array data. This problem is solved by first finding an ensemble of relevant environmental model parameters and the associated posterior probability using a likelihood based inversion of the acoustic array data. In a second step, each realization of these model parameters is weighted with their posterior probability to map into the transmission loss domain. This approach is illustrated using vertical-array data from a recent benchmark data set and from data acquired during the Asian Seas International Acoustics Experiment (ASIAEX) 2001 in the East China Sea. The environmental parameters are first estimated using a probabilistic-based geoacoustic inversion technique. Based on the posterior probability that each of these environmental models fits the ocean acoustic array data, each model is mapped into transmission loss. This enables us to compute a full probability distribution for the transmission loss at selected frequencies, ranges, and depths, which potentially could be used for sonar performance prediction. 相似文献
15.
The problem of fatigue damage estimation of ageing jack-up platforms is considered, using theories of random processes. The sea-wave excitations are modelled as stationary, Gaussian random processes, with specified power spectral density function. The loads acting on the structure due to the sea waves is calculated using Morison’s equation and are therefore non-Gaussian whose probabilistic properties are not available in explicit form. Assuming linear structure behaviour, the probabilistic properties of the structure response are determined using theories of random vibrations. The simple peak counting method is adopted for estimating the mean fatigue damage. This requires knowledge of the joint probability density function of the structure response and its first and second time derivatives, at the same time instant. A methodology has been presented for developing analytical expressions for this joint pdf. This requires evaluation of multidimensional integrals. A recently developed computational algorithm is presented to deal with integrals for which derivation of closed form analytical expressions may not be feasible. The methodology proposed in this paper provides an alternative and computationally cheaper technique for estimating the fatigue damage in comparison to the Monte Carlo simulation procedure. Numerical results have been presented for illustration of the proposed methodology. 相似文献
16.
This study examines the reflection of obliquely incident waves by an infinite array of partially perforated caissons. Based on the linear potential theory, an analytical solution of the present problem was developed by means of the matched eigenfunction expansion method. The solution was obtained in a single strip consisting of the semi-infinite narrow region in front of a caisson and the fluid domain inside this caisson. It was then extended to the whole fluid domain by using the periodicities of the structure and the incident waves along the length of the caissons. The present model was validated by comparing the reflection coefficients of several limiting cases with the corresponding results obtained by previous researchers. Numerical experiments were also conducted to examine the variations of the reflection coefficient versus its main effect factors. The numerical results indicate the differences between the present model and the previous limiting cases, and some helpful results are recommended for practical engineering. 相似文献
17.
In this work, the problem of optimizing the shape of a thin floating plate (sometimes called a dock) to maximize radiation damping is investigated. The plate is modeled with zero draft and floats on the surface of an irrotational, incompressible ocean of infinite extent. For simplicity, only rigid heave motions are considered. The flow problem is analyzed using the Chen and Mei variational principle wherein the potential field inside a hemisphere surrounding the plate is represented using a spherical harmonic expansion and matched on the hemisphere to an outer field described by distributing sources on the hemisphere. The plate shape is parameterized using a Fourier series which is suitable for use with the variational principle. Gradients of the damping coefficient with respect to the shape parameters are developed by solving an adjoint flow problem whose potential is shown to be a scalar multiple of the original flow potential. Optimal plate shapes are determined using the well-known optimization code NPSOL which makes use of the damping coefficient calculation and gradients. 相似文献
18.
State-dependent Riccati equation-based robust dive plane control of AUV with control constraints 总被引：1，自引：0，他引：1
The paper treats the question of suboptimal dive plane control of autonomous underwater vehicles (AUVs) using the state-dependent Riccati equation (SDRE) technique. The SDRE method provides an effective mean of designing nonlinear control systems for minimum as well as nonminimum phase AUV models. It is assumed that the hydrodynamic parameters of the nonlinear vehicle model are imprecisely known, and in order to obtain a practical design, a hard constraint on control fin deflection is imposed. The problem of depth control is treated as a robust nonlinear output (depth) regulation problem with constant disturbance and reference exogenous signals. As such an internal model of first-order fed by the tracking error is constructed. A quadratic performance index is chosen for optimization and the algebraic Riccati equation is solved to obtain a suboptimal control law for the model with unconstrained input. For the design of model with fin angle constraints, a slack variable is introduced to transform the constrained control input problem into an unconstrained problem, and a suboptimal control law is designed for the augmented system using a modified performance index. Using the center manifold theorem, it is shown that in the closed-loop system, the system trajectories are regulated to a manifold (called output zeroing manifold) on which the depth tracking error is zero and the equilibrium state is asymptotically stable. Simulation results are presented which show that effective depth control is accomplished in spite of the uncertainties in the system parameters and control fin deflection constraints. 相似文献
19.
Second-order springing on an elastic body with forward speed is analyzed by numerical simulations. The boundary-value problem for the velocity potential is solved by means of the direct time-domain higher-order boundary element method (HOBEM). The free-surface boundary condition in the boundary-value problem is approximated on the mean surface up to second order by use of perturbation and Taylor-series expansion methods. The body boundary condition for an elastic body is derived with various quantities which are redefined in the generalized mode. These variables such as mode shape, normal vector, etc. are obtained by using directional derivative and continuum mechanics, and the same mathematical expressions are used to obtain several second-order generalized forces. To validate the numerical results, the second-order hydrodynamic force on the bottom-mounted rigid/elastic cylinders without forward speed is compared with other semi-analytic results. The property of second-order forces on an elastic ship is studied by changing the flexural rigidity and forward speed with elastic response. It is confirmed that the second-order velocity potential is important for a body with forward speed and investigation should be made more on numerical methods for accurate computation of the second-order velocity-potential force with forward speed. 相似文献
20.
Cheolsoo Park Woojae Seong Gerstoft P. Siderius M. 《Oceanic Engineering, IEEE Journal of》2003,28(3):468-478
An inversion method using a towed system consisting of a source and two receivers is presented. High-frequency chirp signals that have been emitted from the source are received after multiple penetrations and reflections from the shallow water sub-bottom structure and are processed for geoacoustical parameter estimation. The data are processed such that a good resolution and robustness is achieved via matched filtering, which requires information about the source signal. The inversion is formulated as an optimization problem, which maximizes the cost function defined as a normalized correlation between the measured and modeled signals directly in the time domain. The very fast simulated reannealing optimization method is applied to the global search problem. The modeled time signal is obtained using a ray approach. An experiment was carried out in the Mediterranean Sea using a towed source and receiver system. The inversion method is applied to the experimental data and results are found to be consistent with previous frequency-domain analyses using measurements from a towed horizontal array of receivers and measurements on a vertical array. 相似文献