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A new method for the calculation of wave radiation stress is proposed by linking the expressions for wave radiation stress with the variables in the parabolic mild slope equation. The governing equations are solved numerically by the finite difference method. Numerical results show that the new method is accurate enough, can be efficiently solved with little programming effort, and can be applied to the calculation of wave radiation stress for large coastal areas.
In order to understand the dynamic behavior of submarine pipelines exposed to current and the mechanism of the interaction between current-induced vibration and scour of pipelines on a sandy bottom, an experimental investigation is conducted with a small scale model. A test model which can be tested in the flume is set up by taking into account the typical working conditions of the pipelines and by applying the similarity theory. The interactions between the shape of the scour hole and the behavior of the pipeline as well as the flow patterns of the current are detailed, and the interaction mechanism outlined. The effect of vibration of the pipeline on the development of dynamic scour at different stages is found out. The proposed experimental method and test results provide an effective means for design of marine pipelines against scouring.
Experimental investigation of ice floe breakup on waves by use of non-refrigerated breakable materials has been carried out. The incident wave heights for breakup of ice floe with different lengths, and the influence of rigidity on reflection and transmission coefficients are discussed. The experimental results show that the ratio of the ice floe length, Li, to the wavelength, L, is one of the significant factor affecting the minimum wave height to cause fracture of ice floe, and another key factor is the ratio of the ice floe thickness, ki and Li.
The present study aims to give general hints about hydrodynamic interactions for water wave diffraction on a super large floating structure composed of a large number of box-shaped modules with many small gaps in between. And meanwhile, it also aims to seek for an effective way to take the gap influence into consideration without numerical difficulties existing in conventional methods. An asymptotic matching technique is exploited by virtue of the smallness of gaps. Formal potential solutions are established for the near field around the gap ends and the far field away from gap ends, respectively, and the unknowns in those solutions are uniquely determined by asymptotic matching. The eigen-function expansion method is used for the outer far field and a series of pulsating sources at each gap end is introduced to simulate the gap influence. Strong hydrodynamic interaction is observed and a new resonant phenomenon, the mechanism of which differs absolutely from any known ones, is revealed in the present study. Sharp peak responses for both vertical and horizontal wave-exciting forces on each block are found around some special resonance frequencies, which depend on the draft of the structure and the gap width. The present results are of practical significance to the design of links (connectors) of modules for super large floating structures. And the importance is also closely related to the hydro-elasticity analysis for super large floating structures, in which local loads may be as important as the integrated loads.
With the introduction of the design variables of nodal coordinates, which reflect the embedded depth of the pile and the jacket bed height, a shape optimum design model for offshore jacket platforms is established. A sequential two-level optimum algorithm is developed based on the design variable gradation. On the basis of the finite element method, the sensitivity of the objective function and nodal displacement is analyzed. As an example, the BZ281 oil storage offshore platform, which lies in the Bohai oil field, is designed with the shape optimum model. The results are compared with the cross-section optimum design. The tendency of design variables and its reasons in the two methods are analyzed. In the shape optimum design, the value of objective function is obviously smaller than that of the initial design and the cross-section optimum design. Therefore, the advantage of structure shape optimum design for jacket platforms is remarkable.
According to the fractal theory, the spatial fractal character of coastline is preliminarily discussed on the basis of GIS in this paper. Two aspects are considered: one is the length demarcation of coastline with different scales, and the other is the confirmation of existence of the fractal character on different boundaries of tidal flats. Finally, some significant conclusions are drawn: (1) The coastline of Jiangsu Province has the fractal character and its dimension is 1.0696. (2) It conforms to the exponential correlation between different lengths (L) of coastline and scales (k). It conforms to the formula lgL(k) = -1.029 lgk+ 2.9544 in the continental coastline of Jiangsu province. (3) Different boundaries of a tidal flat have fractal characters, and different fractal dimensions indicate different comparative intensities of erosion and deposition on the tidal flat. (4) The reciprocity between land and sea may affect the value of fractal dimension of a coastline, just as the lithology, substantial constituent and geological structure do.
By use of the hydrodynamic model, the harmonic constants of 8 principal tidal constituents (Q1, O,, P1, K1, N2, M2, S2 and K2) are obtained for the East China Sea, and the harmonic constant of Sa is calculated by two-dimensional interpolation. The calculated results agree well with the observed data around the sea. The harmonic constants can be used to predict the tide in the East China Sea. The cotidal charts of the 9 tidal constituents reveal their distribution.
Summarized in the paper are the author's studies on incipient motion of sediment in recent 40 years. In addition to the forces of gravity, drag and lift, the cohesive force and the additional static pressure are important for fine particles. The relations between three stages of incipient motion are defined by use of instantaneous velocity. Formulas for initial velocity and critical shear stress are given and overall verified by the author's and others' experimental data.
Settling velocity is a fundamental parameter in sediment transport dynamics. For uniform particles, there are abundant formulas for calculation of their settling velocities. But in natural fields, sediment consists of non-uniform particles. The interaction among particles is complex and should not be neglected. In this paper, based on the analysis of settling mechanism of non-cohesive and non-uniform particles, a theoretical model to describe settling mechanism is proposed. Besides suspension concentration and upward turbulent flow caused by other particles, collision among particles is another main factor influencing settling velocity. By introducing the collision theory, equations of fall velocity before collision, collision probability, and fall velocity after collision are established. Finally, a formula used to calculate the settling velocity of non-cohesive particles with wide grain gradation is presented, which agrees well with the experimental data.
The calculation of the temperature field of an underwater concrete tank system storing crude oil is relatively complex. Based on experimental data and optimization analysis of relative parameters, unsteady heat-transfer is calculated by use of heat equilibrium theory. It is found that the predicted value of temperature is in good agreement with experimental data.
In order to examine the effectiveness of engineering protection against localized scour in front of the south groin-group of the Yangtze Estuary Waterway Improvement Project, Phase I , an undistort-ed physical model on a geometric scale of 1:250 is built in this study, covering two groins and their adacent estuarine areas. By use of rinsing fix-bed model as well as localized mobile-bed model, the experiment is undertaken under bi-directional steady flow. According to the experimental results, waterway dredging leads to the increase in steram velocity, the increase being larger during the ebb than during the flood. Construction of the upstream groin has some influence on the flow patterns near the downstream groin. Localized scour in front of the groin-heads is controlled mainly by ebb flow. In the case of a riverbed composed entirely of silt, the depths of localized scour in front of the two groin- heads are 27 m and 29 m, respectively. In reality, the underneath sediment of the prototype riverbed is clay whose threshold velocity is much higher than the stream velocity in the Yangtze Estuary; therefore, the depths of localized scour will not be much larger than the thickness of the silt layer, i. e. 7.4 m and 4.7 m, respectively. The designed aprons covering the riverbed in fron of the groin-heads are very effective in scour control. Aprons of slightly smaller size can also fulfill the task of protection, but the area of localized scour increases significantly.
On the assumption that the vortex and the vertical velocity component of the current are small, a mild- slope equation for wave propagation on non- uniform flows is deduced from the basic hydrodynamic equations, with the terms of (?h h)2 and ? 2h included in the equation. The terms of bottom friction, wind energy input and wave nonlinearity are also introduced into the equation. The wind energy input functions for wind waves and swells are separately considered by adopting Wen's (1989) empirical formula for wind waves and Snyder's observation results for swells. Thus, an extended mild-slope equation is obtained, in which the effects of refraction, diffraction, reflection, current, bottom friction, wind energy input and wave nonlinearity are considered synthetically.
ScholarOne Manuscripts Log In
- Volume 34
- Issue 4
- August 2020
- 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