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Based on theoretical analysis, numerical calculation, and experimental study, this paper discusses breaker indices of irregular waves, transformation of wave spectrum, characteristics and computation of breaking waves, as well as the critical beach slope- under which waves will not break. Computed results are in good agreement with laboratory physical model test data and ocean wave field measurements.
This paper details experiments undertaken in the UK Coastal Research Facility (CRF) at Hydraulics Research (HR), Wallingford. on transformation and run-up of wave trains. The purpose of these experiments is to provide verification data for numerical models of wave transformation in shoaling, surf and swash zones. This is the kind of data that flume experiments are unable to provide, and is collected in the highly controlled environment of CRF where extrinsic factors present in the field are not an issue. The experiments concerning wave trains are undertaken by use of existing wave generation software, and the run-up measurements are made with large experimental run-up gauges.
A study is made on the overshool phenomena in wind-generated waves. The surface displacements of time-growing waves are measured at four fetches in a wind wave channel. The evolution of high frequency waves is displayed with wavelet transform. The results are compared with Sutherland's. It is found that high frequency wave components experience much stronger energy overshool in the evolution. The energy of high frequency waves decreases greatly after overshool.
The basic features and acoustic-physical properties of calcareous seatloor soils in the tropic sea area are obviously different from those of sediments mainly composed of terrigenous materials in the South China Sea. Generally, calcareous soils, composed of carbonate particles of marine organism remains, have the characteristics of high water content, high porosity, low wet density, high sound velocity and greatly varied compressive strength. Recognizing the differences between calcareous soils and terrigenous sediments and engineering geologic significance of calcareous soils is crucial for sea floor geologic research and geolechnical stirvey for pile jacket platform foundation design.
A comprehensive analysis is conducted based on observations on topography, tidal current, salinity, suspended sediment and bed load during the years ot" 1982. 1983. 1988. 1989. 1996 and 1997 in the Yangtze Hstuary. Results show that the deformation of tidal waves is distinct and the sand carrying capacity is large within the mouth bar due to strong tidal currents and large volume of incoming water and sediments. Owing to both temporal and spatial variation of lidal current, deposition and erosion are extremely active. In general a change of up to 0.1 m of bottom sediments takes place during a tidal period. The maximum siltalion and erosion are around 0.2 m in a spring to neap tides cycle. The riverbed is silted during Hood when there is heavy sediment load, eroded during dry season when sediment load is low. The annual average depth of erosion and siltation on the riverbed is around 0.6 m. In particular cases, it may increase to 1.4 m to 2.4 m at some locations.
Based on a linear model of the pressure difference between two sides of a porous wall and the fluid velocity inside it, an analytic solution is established for wave diffraction from a cylinder with an outer porous column and an inner solid column. Numerical experiments are carried out to examine the effects of the wave force on a porous tow-column cylinder and the wave elevations outside and inside the cylinder due to the porous character of the outer column and the ratio between the radii of the inner and outer columns. The numerical results show tha the increase in the coefficient of porosity of the outer column of a double column cylinder will reduce the wave elevation around the cylinder and the wave load on it. The radius of the inner column does not affect too much the wave elevation around the cylinder and the total force on the cylinder.
A new nonlinear dispersion relation is given in this paper, which can overcome the limitation of the intermediate minimum value in the dispersion relation proposed by Kirby and Dalrymple (1986), and which has a better approximation to Hedges'empirical relation than the modified relations by Hedges (1987). Kirby and Dalrymple (1987) for shallow waters. The new dispersion relation is simple in form thus it can be used easily in practice. Meanwhile, a general explicit approximation to the new dispersion relation and other nonlinear dispersion relations is given. By use of the explicit approximation to the new dispersion relation along with the mild slope equation taking into account weakly nonlinear effect, a mathematical model is obtained, and it is applied to laboratory dala. The results show that the model developed with the new dispersion relation predicts wave transformation over complicated topography quite well.
In the paper, a visco-elasto-plastic constitutive model and a method for determining model parameters for soft clay are presented. In this model total strain of soft clay is assumed to he divided into three parts: instantaneous elastic, viseo elastic and visco plastic. The characteristics of instantaneous and visco-elastic deformation of soft clay are simulated by Merchant's model, the plastic is by a model with two yield surfaces. And related constitutive equation is conducted. A number of stress-controlled triaxial tests are performed to calculated the model parameters. The visco-elaslo-plaslic model is used for analysis of (he displacement of an embankment on soft ground by use of three-dimensional finite element method. The predicted settlements agree well with the measured data. It is indicated that the viscous characteristics should he taken into account in deformation analysis for soft clay.
Corrosion of reinforced concrete structures is a serious problem in ocean engineering. As an orientation of study, anticorrosion coating technique is developed and widely applied, but many problems need to be solved. LSW-2 type anticorrosion coating for maritime reinforced concrete structures is characterized by sea water resistance, salt fog resistance, moisture and heal resistance as well as impermeability to chlorions. The new type coating can be applied to wet concrete surface by conventional construction technique. It is a breakthrough in solving the above mentioned problem. The paper mainly introduces the test results, the property indices, coating procedure, construction technique and economic benefit of Ihe coating.
A joint probability density funelion (PDF) for surface slopes in two arbitrary directions is de-rived on the basis of Longuel-Higgins s linear model for three-dimensional (3-D) random wave field, and the correlation moments of surface slopes, as parameters in the PDF. are expressed in terms of direclional spectrum of ocean waves. So long as the directional spectrum model is given, these parameters are deter mined. Since the directional spectrum models proposed so tar are mostly parameterized by Ihc wind speed and fetch, this allows for substituting these parameters with the wind speed and letch. As an example, the wind speed and fetch are taken to he 14 m sand 200km. and the Hasselmann and Donelan directional spectra are respcctively. used to compute these parameters. Some novel results are obtained. One of the interesting results is that the variances of surface slope in downwind and cross-w ind directions determined by the Donelan directional spectra are close to those measured by Cox and Munk (1954). Some discussions are made on these results.
The intertidal flats are classified as "attached bar", "spit" and "isolated bar" in relation to the land, and "broad flat", "sharp bank and "eroded cliff" according to the shape of the cross-shore profile. Tidal currents on the flat are basically back and forth along the river channel banks but gyratory on the seaward side of the Chongming Island. The flow velocity on the intertidal flat is gradually reduced with increasing elevation. The river discharge strengthens ebb flows and modifies current asymmetry especially on the lower flat in neap tide, although hydrodynamics over the tidal flat is tide-dominated. The wave height on the tidal flat is normally limited to a few decimeters although it changes with water depth, slope and wind. Suspended sediment concentration over the tidal flat is typically hundreds to thousands of mg/1. Although the delta has grown rapidly in history, the rate of growth is different in different periods. A maximum advancing rate of 330 m/ a was recently found in the central part of the river mouth towards the sea. In view of the natural conditions, reclamation of higher intertidal flat (above the mean tidal level) in advancing coasts is suggested, which would leave broad wetlands for wild lives. In addition, some possible influences of coastal engineering projects and the future natural backgrounds of engineering under reduction in riverine sediment supply and sea level rise are addressed.
This paper presents an experimental study of a prestressed lightweight concrete platform model with a lank and five steel columns. This platform can be used not only for extraction but also for storage of oil and is suitable lor the Bohai Sea and other shallow seas of China. The platform is subjected to temperature, load, or both. The corresponding temperature distribution, strains, cracks, and vulnerable parts of the platform are analyzed respeetively. By use of the finite element method and empirical formulas, the temperature field of the model is analyzed. The results agree with the experimental results, thereby veri tying the reliability of these two calculating methods. The paper provides an experimental basis for the design of the bearing capacity and normal service slate of prcslressed concrete platforms.
Incremental harmonic balance method (IHBM) is applied to geometrically nonlinear vibration analysis of a simply supported pipe conveying fluid, the material of which is viscoelaslic of the Kehin Voigt type. Some unstable phenomena - the appearance of the peak or jumps in the pipe's amplitude-frequency curves, which are considered to be of importance to this kind of structure, are pres enled in the numerical results, and the influence of several parameters of the system on the dynamic characteristic of the pipe are also studied. It is believed that this is the first attempt to search for the periodic solution of the pipe and its intrinsic properly with such a method.
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- 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