Model Simplification and Parameter Modification for Offshore Platforms Using Experiment Data

- In this paper, a computation method has been developed so as to compare the finite element method (FEM) with the test results directly. The structure is divided into the "master" and "slave" degrees of freedom. The simplified model can be obtained with modal reduction. Then the design sensitivity analysis of the eigenvalues and eigenvectors has been carried out using the modal frequency and modal shape of the test. A two-story frame structure and a jacket model structure have been calculated. Meanwhile, the modified coefficient, the FEM computational and experimental values have been given. It has been shown that the FEM model modified using the test modal value is efficient.     

Study on First-Yield Collapse of Submarine Pipelines

-The first-yield collapse of submarine pipelines with an initial out-of-roundness imperfection un-der combined bending and external pressure load is formulated by means of the Von.Mises yield criterion.The formula reduces to Timoshenko and Gere's expression in the case of external pressure load alone.Theinfluence curves of various parameters on the yield strength are presented,the collapse of submarinepipelines in a deep water region is numerically predicted,and the effect of pre-yield nonlinear bending onthe yield strength is also examined.     

Numerical Analysis of Factors Influencing Implosion

-By using gas-liquid two-phase flow theory, a modified mathematical model based on the computational fluid dynamics method SIMPLE (Semi-Implicit Method for Pressure-Linked Equations) is introduced to investigate implosion phenomena in high pressure chambers systematically. A theoretical simulation-prediction method, which is independent of experimental data, is developed in the paper and great improvement has been made on the topic. In the paper, various implosion situations have been simulated and predicted. Effects of a series of factors influencing implosion results and methods of reducing implosion danger have been analysed. The analysis results are of importance to underwater engineering practice.     

Numerical Modeling of Wave and Current Interaction in the Tidal Inlet Area

This paper investigates the phenomena of wave refraction and diffraction in the slowly varying topography, as well as the current deflection due to wave actions. A numerical model is developed based on depth integrated mean continuity equation and momentum equations, and a 3rd-order wave equation which governs the wave diffraction, refraction and interaction with current. Examples to examine the above model are given comparing with the laboratory data or the numerical results of other researchers. An example simulating the inlet area shows the interesting velocity field which may be used as a pioneer to further study on the nearshore hydrodynamics and sedimentation.     

Efficiency removal of phenol, lead and cadmium by means of UV/TiO2/H2O2 processes

A variety of processes can be used in treatment of industrial wastewaters. The relatively newest of which is photo catalysis with titanium dioxide which may also be used plus hydrogen peroxide to improve the treatment rate. In this study, photo catalysis/ hydrogen peroxide processes had been employed for the removal of phenol, lead and cadmium by three different pHs of 3.5, 7 and 11. The treatment tests were also accomplished without UV irradiation. In both experiments, the variables were pH and concentrations of reagent chemicals, but the detention time was kept constant (180 min). Results indicated that the optimum efficiencies of phenol and Cd removal were 76 % and 97.7 % at pH=11, respectively, and for lead, it was 98.8% in all pHs. In other words, no pH dependency was regarded for lead treatment. These results were all obtained by simultaneous use of UV irradiation with 3 mL/L H₂O₂ and 0.8 g/L TiO₂. Finally, the best pH for treatment, when all the three contaminants are presented is considered to be at 11. These results should be regarded by all industrial treatment plants which have experienced the problem of these three special contaminants in their effluents.     

Patterns of deposition from experimental turbidity currents with reversing buoyancy

Turbidity currents are turbulent, sediment‐laden gravity currents which can be generated in relatively shallow shelf settings and travel downslope before spreading out across deep‐water abyssal plains. Because of the natural stratification of the oceans and/or fresh water river inputs to the source area, the interstitial fluid within which the particles are suspended will often be less dense than the deep‐water ambient fluid. Consequently, a turbidity current may initially be denser than the ambient sea water and propagate as a ground‐hugging flow, but later reverse in buoyancy as its bulk density decreases through sedimentation to become lower than that of the ambient sea water. When this occurs, all or part of the turbidity current lofts to form a buoyant sediment‐laden cloud from which further deposition occurs. Deposition from such lofting turbidity currents, containing a mixture of fine and coarse sediment suspended in light interstitial fluid, is explored through analogue laboratory experiments complemented by theoretical analysis using a ‘box and cloud’ model. Particular attention is paid to the overall deposit geometry and to the distributions of fine and coarse material within the deposit. A range of beds can be deposited by bimodal lofting turbidity currents. Lofting may encourage the formation of tabular beds with a rapid pinch‐out rather than the gradually tapering beds more typical of waning turbidity currents. Lofting may also decouple the fates of the finer and coarser sediment: depending on the initial flow composition, the coarse fraction can be deposited prior to or during buoyancy reversal, while the fine fraction can be swept upwards and away by the lofting cloud. An important feature of the results is the non‐uniqueness of the deposit architecture: different initial current compositions can generate deposits with very similar bed profiles and grading characteristics, highlighting the difficulty of reconstructing the nature of the parent flow from field data. It is proposed that deposit emplacement by lofting turbidity currents is common in the geological record and may explain a range of features observed in deep‐water massive sands, thinly bedded turbidite sequences and linked debrites, depending on the parent flow and its subsequent development. For example, a lofting flow may lead to a well sorted, largely ungraded or weakly graded bed if the fines are transported away by the cloud. However, a poorly sorted, largely ungraded region may form if, during buoyancy reversal, high local concentrations and associated hindered settling effects develop at the base of the cloud.