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In the present study,the surface elevation of wind waves oberved in laboratory and in the Bohai Sea are adopted for the estimation of the wind wave frequency spectrum by use of the method of the arcsine law(MAL).The traditional method uses the surface elevation to calculate the correlation and then estimate the frequency spectrum while the MAL,presented by Yu and Lan(1979),uses the time sequence of zero-crossing points of surface elevation rather than directly the surface elevation to calculate the correlation.66 sets of wind wave data obtained in laboratory and 420 sets of data observed in the Bohai Sea are adopted for the examination of the method introduced by Yu and Lan.Results show that the MAL can give reliable estimation of wind wave spectra.Correlation and form of spectra estimated by the MAL are similar to those estimated by the traditional method.The peak frequency and the spectral density in peak frequency by the MAL are close to those obtained by the traditional method.
In the present study,the flow field around a circular pier is investigated with experimental measurements and numerical simulations.The transient flow patterns during erosion are studied in detail.The results show that the traditional equations of particle motion are not perfect for the calculation of the sand motion under this complex flow situation.The scouring agents,such as turbulent intensity,the fluctuating pressure and the vertical pressure gradient,having many effects on the sand motion with the increasing scouring depth,need to be considered in modifying the traditional model.
Several ray-type 1D and 2D KdV equations for two-layer stratified ocean with topographic effect are derived in detail in the present study.A simplified version of these equations,ray type 1D KdV equation,is used to calculate numerically the disintegration of initial interface soliton from the deep sea to the continental shelf.At the same time,a laboratory experiment is carried out in a 2D stratified flow and internal wave tank to examine the numerical results.A comparison of the numerical results with the experimental results shows that they are in good agreement.The numerical results also show that the ray-type KdV equation has high accuracy in describing the evolution of initial interface waves in shelf/slope regions.Form these results,it can be concluded that the fission process is a dominant generating mechanism of interface soliton packets on the continental shelf.
Based on the dynamic theories of water waves and Mindlin plates,the analytic solution of interaction between surface waves and two-dimensional floating elastic plates with edge-restraint is constructed by use of the Wiener-Hopf technique.Firstly,without regard for elastic edge restraint,the wave-induced responses of elastic floating plate analyzed by the present method are in good agreement with the results from literature and experimental results.Therefore,it can be shown that the present method is valid.Secondly,three end-restraint cases(i.e.,the left-end elastic restraints,the both-end elastic restraints,and the right-end elastic restraints)are proposed to reduce the vibration of floating plates,in which the spring is used to connect the sea bottom and the floating plate's left(or right)edge.The relations between the spring stiffness and the parameters of wave-induced responses of floating plates are discussed.Moreover,the effective method to reduce the vibration of floating elastic plates can be obtained through comparison.
The spectral methods and ice-induced fatigue analysis are discussed based on Miner's linear cumulative fatigue hypothesis and S-N curve data.According to the long-term data of full-scale tests on the platforms in the Bohai Sea,the ice force spectrum of conical structures and the fatigue environmental model are established.Moreover,the finite element model of JZ20-2MSW platform,an example of ice-induced fatigue analysis,is built with ANSYS software.The mode analysis and dynamic analysis in frequency domain under all kinds of ice fatigue work conditions are carried on,and the fatigue life of the structure is estimated in detail.The methods in this paper can be helpful in ice-induced fatigue analysis of ice-resistant platforms.
This paper thoroughly studies a control system with control allocation for a manned submersible in deep sea being developed in China.The proposed control system consists of a neural-network-based direct adaptive controller and a dynamic control allocation module.A control energy cost function is used as the optimization criteria of the control allocation module,and weighted pseudo-inverse is used to find the solution of the control allocation problem.In the presence of bounded unknown disturbance and neural networks approximation error,stability of the closed-loop control system of manned submersible is proved with Lyaponov theory.The feasibility and validity of the proposed control system is further verified through experiments conducted on a semi-physical simulation platform for the manned submersible in deep sea.
A numerical model is developed by use of the boundary integral equation method to investigate the responses of a two-dimensional floating structure.The structure under consideration consisting of two pontoons,is connected by a rigid framework,and linked to the sea floor by a mooring system.The theoretical conception is based on potential theory with linear external forces,and applied to an arbitrarily shaped body and water depth.The discussion includes the influence of draft and space between pontoons on the responses of the floating structure.Finally,the validity of the method is adequately verified by experimental results.
The dynamic analysis of a pipe system is one of the most crucial problems for the entire mining system.A discrete element method(DEM)is proposed for the analysis of a deep-ocean mining pipe system,including the lift pipe,pump,buffer and flexible hose.By the discrete element method,the pipe is divided into some rigid elements that are linked by flexible connectors.First,two examples representing static analysis and dynamic analysis respectively are given to show that the DEM model is feasible.Then the three-dimensional DEM model is used for dynamic analysis of the mining pipe system.The dynamic motions of the entire mining pipe system under different work conditions are discussed.Some suggestions are made for the actual operation of deep-ocean mining systems.
In engineering practice,tubular X-joints have been widely used in offshore structures.The fatigue failure of tubular X-joints in offshore engineering is mainly caused by axial tensile stress.In this study,the stress concentration factor distribution along the weld toe in the hot spot stress region for tubular X-joints subject to axial loads have been analyzed by use of finite element method.Through numerical analysis,it has been found that the peak stress concentration factor is located at the saddle position.Thereafter,80 models have been analyzed,and the effect of the geometric parameters of a tubular X-joint on the stress concentration factor has been investigated.Based on the experimental values of the numerical stress concentration factor,a parametric equation to calculate the stress concentration factor of tubular X-joints has been proposed.The accuracy of this equation has been verified against the requirement of the Fatigue Guidance Review Panel,and the proposed equation is found capable of producing reasonably accurate stress concentration factor values for tubular X-joints subject to axial loads.
To study ice-induced vibration of a compliant conical structure,a series of model tests were performed from 2004 to 2005.In the tests,the ice sheet before the compliant conical structure was found to fail in two-time breaking.From 2005 to 2006,this type of ice failure was studied through more groups of tests.The tests show that two-time breaking is the typical failure of ice before steep conical structures,and is controlled by other factors at the same time,such as ice speed and the angle of the cone.
In this study,an FEM-SBFEM(scaled boundary finite element method)coupling procedure proposed by Fan et al.(2005)is adopted to obtain the dynamic responses of a submerged cylindrical shell subjected to plane step or exponential acoustic shock waves.The coupling procedure can readily be applied to three-dimensional problem,however for clarity,the problems to be presented are limited to two-dimensional domain.In the analyses,the cylindrical shell is modeled by simple beam elements(using FEM),while the effects of the surrounding infinite fluid is modeled by the SBFEM.In it,no free surface and seabed are involved.Compared with Fan and his co-authors' works,the FEM-SBFEM coupling procedure is further verified to be feasible for shock waves by benchmark examples.Furthermore,parametric studies are performed and presented to gain insight into effects of the geometric and material properties of the cylindrical shell on its dynamic responses.
A finite-difference approach is used to develop a time-dependent mild-slope equation incorporating the effects of bottom dissipation and nonlinearity.The Euler predictor-corrector method and the three-point finite-difference method with varying spatial steps are adopted to discretize the time derivatives and the two-dimensional horizontal ones,respectively,thus leading both the time and spatial derivatives to the second-order accuracy.The boundary conditions for the present model are treated on the basis of the general conditions for open and fixed boundaries with an arbitrary reflection coefficient and phase shift.Both the linear and nonlinear versions of the numerical model are applied to the wave propagation and transformation over an elliptic shoal on a sloping beach,respectively,and the linear version is applied to the simulation of wave propagation in a fully open rectangular harbor.From comparison of numerical results with theoretical or experimental ones,it is found that they are in reasonable agreement.
Wave induced excess flow of momentum(WIEFM)is the averaged flow of momentum over a wave period due to wave presence,which may also be called 3-D radiation stress.In this paper,the 3-D current equations with WIEFM are derived from the averaged Navier-Stokes equations over a wave period,in which the velocity is separated into the large-scale background velocity,the wave particle velocity and the turbulent fluctuation velocity.A concept of wave fluctuating layer(WFL)is put forward,which is the vertical column from the wave trough to wave ridge.The mathematical expressions of WIEFM in WFL and below WFL are given separately.The parameterized expressions of WIEFM are set up according to the linear wave theory.The integration of WIEFM in the vertical direction equals the traditional radiation stress(namely 2-D radiation stress)given by Longuet-Higgins and Stewart.
ScholarOne Manuscripts Log In
- Volume 33
- Issue 6
- December 2019
- Superintended by:
CHINA ASSOCIATION FOR SCIENCE AND TECHNOLOGY
- Sponsored by:
Chinese Ocean Engineering Society （COES）
- Edited by:
Nanjing Hydraulic Research Institute
Adaptive Predictive Inverse Control of Offshore Jacket Platform Based on Rough Neural Network
Numerical Simulation of Water Exchange Characteristics of the Jiaozhou Bay Based on A Three-Dimensional Lagrangian Model
A Global Reliability Assessment Method on Aging Offshore Platforms with Corrosion and Cracks