Perturbation Analysis of the Attached Water Mass Effect on Offshore Platform Dynamic Response

- Theoretically speaking, it is impossible to make the differential equation of motion uncoupled for the natural modes of a system in consideration of the attached water. The hydro-elastic structure is equal to the, non-proportional damping system. In this paper a perturbation analysis method is put forward. The structure motion equation is strictly solved mathematically, and the non-proportional damping problem is transformed into a series of proportional damping ones in the superposition form. The paper also presents the calculation formula of the dyanamic response of the structure being subjected to harmonic and arbitrary load. The convergence of the proposed method is also studied in this paper, and the corresponding convergence conditions are given. Finally, the proposed method is used to analyze the displacement response of a real offshore platform. The calculation results show that this method has the characteristics of high accuracy and fast convergence.     

西沙群岛星虫类研究Ⅱ——管体星虫属一新种

The present paper is the second part of a series of studies on the Sipunculoids of the Xisha Islands,South China Sea. In 1982, nine species including Siphonosoma cumanense (Keferstein) (Sato, 1939 locality is Taiwan) is identified belonging to six genera and recorded by the author.In this paper, regarded as a new species, the Siphonosoma nanhaiensis is descibed with a morphologically comparison with other 5 species of the very genus found in Indo-Pacific region.     

Rain-Flow and Reverse Rain-Flow Counting Method for the Compilation of Fatigue Load Spectrum

The rain-flow counting method is widely used to compile the fatigue load spectrum. The second stage counting of the rain-flow method is a troublesome process. In order to overcome this drawback, the rain-flow and reverse rain-flow counting method is proposed in this paper. In this counting method, the rule for counting of the rain-flow method is modified, so that the sequence of load-time need not be adjusted. This is a valid and useful method to count cycles and compile the load spectrum and it can be widely used in ocean engineering.     

Biochemical Mechanism of the Eutrophication and Its Prevention—the Deep Treatment of Waste Water and Its Denitrification and Dephosphorization

Biochemical mechanism of forming the red tide is discussed in this paper.The existence of a large number of nitrates and phosphates in the eutrophic water is the prerequisite of explosive increase of algae and the forming of red tide.Reduction of eutrophication is an important approach to preventing the red tide.The method of deep treatment of the waste water and its denitrification and dephosphorization are introduced,and a new opinion on the red tide formation and fundamental prevention is put forward.     

NUMERICAL CALCULATION OF HYDRODYNAMIC COEFFICIENT FOR A FLOATING BODY IN WAVES

A preliminary numerical model of the buoyant drum by wave action is presented, which is based on The Finite Boundary Element Method of the source distribution. A series formula of Green's function is used for the derivation of the model. In the paper the calculated results of the examples for a sphere and a buoyant drum are close to the data in some references. A subject of great interest to ocean engineers is the response a floating body suffers in ocean waves. In this paper, the oscilatory motion of a buoyant drum is analysed and a calculating method is presented. Applying this calculating method, the hydrodynamic coefficient for any kind of floating bodies can be obtained.     

Some Considerations in Design and Construction of the Wei-Liu Water Supplying Submarine Pipeline

The Wei- Liu water supplying submarine pipeline is at present the longest one of the kind in China. It is about 4 kilometers long from Weihai City to Liugong Island in Shandong province. It took only half a year to design and construct it. The project was of a high economic efficiency and some practical experiences were achieved. In this paper a general introduction to the design and construction of this pipeline is presented and such problems as the stability of the pipeline in very soft clay, design of curved slide for launching and estimation of dragging forces are expounded.     

The Nonlinear Wave Force on a Circular Cylinder in Shallow Water

Based on the 1st order cnoidal wave theory, the nonlinear wave diffraction around a circular cylinder in shallow water is studied in this paper. The equation of the wave surface around the cylinder is formulated and by using this formula the wave surface elevation on the cylinder surface can be obtained. In this paper, the formula for calculating the cnoidal wave force on a circular cylinder is also derived. For the wave conditions which are often encountered in practical engineering designs, the ratios of the nonlinear wave forces to the linear wave forces are calculated, and the results are plotted in this paper for design purposes. In order to verify the theoretical results, model tests are conducted. After comparing the test results with the theoretical ones, it is concluded that, in shallow water, for the case of T g / d~(1/2) > 8-10 and H / d > 0.3, the cnoidal wave theory should be used to calculate the wave action on a cylindrical pier.     

Reliability Analysis for Offshore Platform Structural Systems

A system reliability estimation method for spatial jacket platforms is developed in this paper,The jacket platform is modeled into three-dimensional assembly of spatial beam and plate elements in Fi-nite Element Method(FEM).The limit failure states correspond to collapse of a series of structural mem-bers which are identified by engineering design criteria.In this paper the following aspects are taken intoaccount:the punching shear and buckiing failures in member failure modes for the tubular joints and tubu-lar columns respectively;incremental loading approach for establishment of the safety margin equations ofsystem failure;the algorithm of enumerating significant failure modes for the structural systems and otherconcepts,such as the false failure mode and the virtual limit state.The final work is devoted to the reliabili-ty analysis for a practical jacket platform presently put into operation on the Bohai Sea.The computed re-sults shows that method suggested in this paper is feasible and effective for     

The transient response of an ocean to moving wind field

The paper studies the short period response of an unbounded and uniform ocean to moving wind field. Firstly, it is shown that the response disturbance has two kinds of motion, one is geostrophical and other is inertial gravity wave. Secondly, this paper studies the disturbance source caused by a circular wind field which moves rapidly in a straight path on a horizontal plane. It is shown that the disturbance source is mainly determined by the distribution of the curl of wind stress. Thirdly, this paper studies the solution of disturbance equation with nonhomogeous term of disturbance source as an impulse. It is shown that the oceanic response is determined by disturbance source. Finally, by calculating numerically the current velocity and surface elevation in time, it is shown that the intensity, spatial scale and duration of the response are closely related to wind field.     

Discharge Control on Boundary of Tidal Models and Measuring Techniques of Low Current Velocity

This paper describes the discharge control technique on boundary used in two models, one is the model of hot water drainning in Dayawan Nyclear Power Plant, Guangdong, and the other is the model for trainhing the sand bar at the Guanhe Estuary, Jiangsu. Many years of application shows that this technique has the advantages of good reliability, repeatability and validity. The speedometer of hydrogen bubble is also introduced in this paper. The device can display and store tracing lines in a computer, and help operators to obtain the value and direction of transient velocity of a nonsteady current, thus, the problem of measurment of low current velocity in tidal model tests is solved and the automation of the measurement of current velocity is realized.     

The application of Hartley transform to ocean engineering

The Hartley transform is a real integral transform based on harmonic functions and hassome characteristics similar to the Fourier transform. Most applications in ocean engineering requiring the Fourier transform can also be performed by the Hartley transform. The fast Hartley transform is twice faster and more convenient to handle than the corresponding fast Fourier transform, so it is a real valued alternative to the complex Fourier transform in many applications. The use of the Hartley transform in ocean engineering is presented in detail in this paper, including wave spectral analysis, separation of waves, cross-correlation in PIV technique and expression of equation in the Hartley domain. The examples in the paper show deeply the advantage and efficiency of the Hartley transform over the Fourier transform.     

REPRODUCTIVE BEHAVIOUR AND EARLY EMBRYONIC DEVELOPMENT OF Trachypleus tridentatus

This paper reports the season, environmental conditions and pattern of spawning, fecundity and hatching amount of king crab, Trachypleus tridentatus. The egg-diameter of this animal has seasonal variations, which is different from that reported in foreign countries. The egg cleavage of the animal is in the transitional pattern from holoblastic cleavage to surface division. Egg cleavage occurs firstly on one pole with false cleavage furrows, the number of division nucleus increases continuously which move outward from the yolks to form into a layer of blastomere on the surface of the blast together with some of egg plasma. The blastomere formed into the blastoderm and the polygonal cells encircled in this cell layer is equal to the "yolk cells" of insects during the period of egg cleavage. The formation of the periblas-tula is the result of egg cleavage. This paper makes application of the technique of vital staining in exploring the properties of the stained particles. The death of the blasts after stai     

Structural Model Updating of Jacket Platform by Control Theory Using Vibration Measurement Approach

The identification of variations in the dynamic behavior of structures is an important subject in structural integrity assessment.Improvement and servicing of offshore platforms in the marine environment with constant changing,requires understanding the real behavior of these structures to prevent possible failure.In this work,empirical and numerical models of jacket structure are investigated.A test on experimental modal analysis is accomplished to acquire the response of structure and a mathematical model of the jacket structure is also performed.Then,based on the control theory using developed reduction system,the matrices of the platform model is calibrated and updated.The current methodology can be applied to prepare the finite element model to be more adaptable to the empirical model.Calibrated results with the proposed approach in this paper are very close to those of the actual model and also this technique leads to a reduction in the amount of calculations and expenses.The research clearly confirms that the dynamic behavior of fixed marine structures should be designed and assessed considering the calibrated analytical models for the safety of these structures.     

Longshore Current on an Equilibrium Beach

Natural beaches tend to be concave-up rather than planar and are reasonable to be modeled by an equilibrium beach profile. A governing equation for longshore current on an equilibrium beach is derived and its analytical solution is given in this paper. Through comparisons of the present solution and field data of longshore current for a step-type beach, the present solution is found to have fairly agreeable prediction to longshore current inside the surf zone. The effects of the shape of a concave-up beach and turbulent mixing stress on longshore current inside the surf zone are discussed in the present paper.     

Dissipation source function and an improvement to LAGFD-WAM model

In this paper, a new theoretical expression of dissipation term is presented on the basis of statistical model of breaking wave, which is an improvement to LAGFD-WAM wave model. The computational results in three typical wind fields show a good improvement to LAGFD-WAM model and a better accuracy in comparison with the observed data in the South China Sea.     

DETERMINATION OF SECTION THICKNESS AND REASONABLE PRESTRESSING FORCE OF PRESTRESSED CONCRETE SUBMARINE OIL STORAGE TANKS

In this paper, based on the research of F. K. Kong[1] and considering the special features of submarine oil storage tanks, formulae for calculation of the minimum section thickness of oil tanks and simplified formulae for calculating tendon area of the tank are proposed. The main idea of these formulae is to determine the prestressing force more reasonably. An example is given to illustrate the steps of calculation. According to the method proposed in this paper, the trouble of repeated corrections of section thickness and tendon area is avoided and a short-cut method of choosing the best design is proposed.     

Design, Optimization and Numerical Modelling of A Novel Floating Pendulum Wave Energy Converter with Tide Adaptation

A novel floating pendulum wave energy converter (WEC) with the ability of tide adaptation is designed and presented in this paper. Aiming to a high efficiency, the buoy''s hydrodynamic shape is optimized by enumeration and comparison. Furthermore, in order to keep the buoy''s well-designed leading edge always facing the incoming wave straightly, a novel transmission mechanism is then adopted, which is called the tidal adaptation mechanism in this paper. Time domain numerical models of a floating pendulum WEC with or without tide adaptation mechanism are built to compare their performance on various water levels. When comparing these two WECs in terms of their average output based on the linear passive control strategy, the output power of WEC with the tide adaptation mechanism is much steadier with the change of the water level and always larger than that without the tide adaptation mechanism.     

ANALYSIS OF PIPELINE BEHAVIOURS DURING LAYING OPERATION

On the S-lay pipeline analysis, the stiffened catenary method which usually can only be used to determine the configuration of sag-bend of pipeline is now expanded to solve that on the total length of pipeline in the first part of this paper. In the second part, a finite difference procedure of S-lay analysis is presented, which is successfully used to solve 2-D problem with a consideration of current load and the effects of inclination as well as elasticity of sea bed as shown in dimensionless curves and some examples.     

On Spatial Fractal Character of Coastline——A Case Study of Jiangsu Province,China

According to the fractal theory,the spatial fractal character of coastline is preliminarily dis-cussed on the basis of GIS in this paper.Two aspects are considered:one is the length demarcation ofcoastline with different scales,and the other is the confirmation of existence of the fractal character on dif-ferent boundaries of tidal flats.Finally,some significant conclusions are drawn:(1)The coastline ofJiangsu Province has the fractal character and its dimension is 1.0696.(2)It conforms to the exponentialcorrelation between different lengths(L)of coastline and scales(k).It conforms to the formula lgL(k)=-1.029lgk+2.9544 in the continental coastline of Jiangsu province.(3)Different boundaries of a tidal flathave fractal characters,and different fractal dimensions indicate different comparative intensities of ero-sion and deposition on the tidal flat.(4)The reciprocity between land and sea may affect the value offractal dimension of a coastline,just as the lithology,substantial constituent and geological s     

ANALYSIS OF DYNAMIC STABILITY OF SUBMERGED STRUCTURE

The submerged structure is basically a large three-dimensional structure of few statically redundant members. The structure is subjected to vertical dead and live loads in addition to the wave forces. An analysis of dynamic stability of the submerged structure without damping has been made by J. Thomas and Abbas (1980). In this paper the analyses of dynamic stability of the sumberged structure with damping are conducted. The case structure with damping is more complicated 'than the case without it. According to the principle of perturbation, a new model for dynamic stability calculation in consideration of damping effect is developed. In this paper, the formulas are deduced, the computational program is compiled, the practical examples are analysed, and this problem is solved very satisfactorily. The computational results show that the shape and value of the regions of dynamic instability can be changed significantly by damping. So only by considering damping can the property of dynamic stability of the submerged structure be reflected correctly.