Taiwan is usually invaded by typhoons during the summer and autumn seasons. When a typhoon approaches the coast, the strong wave energy combined with a large amount of discharge from the rivers usually reforms the morphology around the estuaries. This study integrated numerical simulation and field survey to analyze the mechanism of sediment transport around the Taimali river estuary. The effect of the coastal sediment transportation, the suspended load of the river, as well as the change of the bathymetry, were all taken into consideration. The simulated change of the bathymetry agrees readily with the results of the survey. The successful practice of methodology in assessing the coastal evolution could be very helpful on integrated coastal management.
This paper provides a mathematical model for accurate and efficient calculation of the elongation of each string within a pipe-in-pipe top tensioned riser system due to gravity, pressure and thermal expansions. The resulting riser system elongation effect is subsequently derived considering the interactions among all riser strings. In the case where a tensioner exists, its nonlinear relationship between tension force and displacement can be captured by using an iterative calculation method. Examples show that the approach is efficient, and this mathematical framework is capable of calculating the riser system tension as well as distributing tension to each string. With the proposed approach, inner riser pipe pretension can be determined efficiently considering load conditions during the life time of the riser system.
As understanding in the management of Floating Offshore Installations (FOIs) has grown across the offshore Oil & Gas industry, so too has an appreciation of the criticality of FOI hull structures.
Previously the hull was seen by many operators as merely the platform upon which the process equipment was located. The hull condition was considered as low risk. The hull had, after all, been designed and constructed to Classification Society Rules which stemmed from over 200 years of experience with ocean going vessels.
However, the philosophy in Class Rules is that the hull undergoes a robust five yearly cycle of surveys to confirm and assure its continued integrity. Part of that cycle includes drydocking the vessel. Unfortunately, as the industry is well aware, an FOI is not as easy to drydock as a trading ship and indeed when drydocking has proved necessary, the costs and production deferment has been considerable. This has resulted in significant challenges to operators in managing the hull integrity of their floating installations.
Since in some offshore jurisdictions, Classification is not mandatory, some operators have chosen not to class their assets and instead extend the concepts of structural integrity management and have sought to develop techniques to inspect the submerged hull and the internal cargo and ballast tank structures themselves.
Inspection techniques and the information obtained there from are key parameters in the assessment of structural integrity. But are these parameters well identified? What data is needed to assure hull integrity? What is the best way to obtain this data? Will the data gathered assure class and/or regulatory compliance?
Prediction of extreme loads by statistical extrapolation, using short-term distributions to obtain the long-term distribution, is crcucial for offshore wind turbines. According to the requirements of the IEC61400-3, data from simulations of four types of 5MW offshore wind turbines are obtained. The three models, global maximum, block maximum and peak-over-threshold, are used respectively to fit Gumbel distribution to predict structual loads in the long term, with results compared, verifying the comparative rationality of the block maximum method. In the discussion of different block sizes, the appropriate block size is recommended, thus providing references for offshore wind turbines load calculation in the long term.
Hydrodynamic aspects on three-dimensional effects were investigated in this study for simple and convenient conversion of tidal stream energy using a Vertical-Axis Turbine (VAT). Numerical approach was made to reveal the differences of flow physics between 2-D estimation and rigorous 3-D simulation. It was shown that the 3-D effects were dominant mainly due to the variation of tip vortices around the tip region of rotor blade, causing the loss of lift for the reduction of torque for rotating turbine blade. A VAT with supporting circular discs at both ends spanwisely was then proposed to reduce the three-dimensionality and increase the structural strength as well as the power coefficient.
Numerical simulations are performed to investigate the velocity, streamlines, vorticity and turbulent kinetic energy perturbations around a porous triangular submerged breakwater, as the breaking Stokes waves of different height passed over it. The coupling of wave interaction with the porous medium is established based on solutions of two dimensional Reynolds Averaged Navier-Stokes (RANS) equations in a Cartesian grid in combination with K-ε closure and the VOF method. The simulations reveal ‘clockwise’ and ‘anticlockwise’ rotation of the fluid below the trough and crest of the viscous waves, and the patterns extended deep inside the porous structure. Two different values of porosity parameter and a non-porous case have been studied to better understand their influence on the physical flow behavior in and around the breakwater. Interestingly, the turbulent kinetic energy in the vicinity of the wave crest was found decrease by about 75% following interaction with the porous structure, as compared with the corresponding non-porous case. The stability and accuracy of the numerical model have been ascertained extensively through a number of comparisons with existing laboratory experiments and the well established theoretical predictions.
The support structure for an offshore wind turbine is a significant contributor to the total project cost, typically contributing up to 20% of the CAPEX. Optimization and cost savings in the area of support structure design may therefore yield sizeable reductions in the overall cost of energy for offshore wind. The typical method used for the design of offshore structures utilizes a sequential or partially integrated modelling approach, with the wind loads and wave loads applied to the structure within separate tools in sequential phases. This paper investigates the cost benefits associated with the use of an integrated design approach, with the full loading environment applied in a single phase in conjunction with advanced turbine control techniques.
Tsuru, Eiji (Nippon Steel & Sumitomo Metal Corporation) | Shinohara, Yasuhiro (Nippon Steel & Sumitomo Metal Corporation) | Nagai, Kensuke (Nippon Steel & Sumitomo Metal Corporation) | Nagata, Yukinobu (Nippon Steel & Sumitomo Metal Corporation) | Hamatani, Hideki (Nippon Steel & Sumitomo Metal Corporation)
Bending deformability is required for line pipes used in reeling lay (R-lay) methods in which the pipes are reeled and unreeled on spools. This study describes the reelability of a girth-welded pipe, evaluated by the full-scale bending test and FEA simulation. These approaches demonstrate that the strength difference between the girth-welded pipes increases the possibility of local buckling while the strength variation in the circumferential direction is not detrimental to reelability. The results of this study, especially the investigation of fracture mechanism in reeling, demonstrate non-heat-treated (NHT) ERW line pipe can be used for R-lay.
In the present paper a recently installed Sensor Network for Monitoring the Response (SNMR) of a Floating Structure (FS) is presented. SNMR is deployed on a pontoon-type FS operating as a floating breakwater, located 300m from the coast in the port of Neos Marmaras in Greece. The developed SNMR consists of: (i) sensors for real time measurement of FS’s critical response quantities related with the structural integrity and safety of the FS as well as of environmental parameters and (ii) data acquisition and data transfer and storage system. Characteristic examples of time series of the measure quantities obtained during the operation of the SNMR are presented and preliminary assessed.
In this paper, a high-speed displacement vessel is proposed and the effects of bowshapes on hydrodynamics are studied. Ten types of hull forms based on the NPL 4b are created and their seakeeping and resistance performances are investigated and discussed. Since ships are commonly slender body, a seakeeping calculating code based on the STF strip method, which could give reasonable trend predictions, is developed. In the following calculations, four hull types are selected for further study: the original one (‘A-C NPL’), the bare vertical bow one (‘B-B a’), the AXE one (‘B-B b’) and the wave piercing one (‘C-A’). The calm water wave resistance performances of all hulls are calculated in both deep waters and restricted waters by adopting a code based on potential theory. Moreover, a more accurate code considering water viscosity is employed to compute the responses of different types of hulls in waves. Finally, the simulation results and the accuracy of the potential theory code and CFD code are analyzed.