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Abstract In order to limit the destruction and reduce the loss of life in future tsunamis, it is essential that people in areas at risk are made aware of this risk and given the opportunity to prepare and evacuate to higher ground prior to the deluge. Tsunami Early Warning Systems (EWS) are introduced for this purpose. These systems measure the tsunami risk associated with an underwater earthquake event and give an early indication to those regions at risk of the arrival time of the tsunami. Systems of this nature have already been successfully implemented in the Pacific Ocean. A modern EWS often consists of several DART (Deep-ocean Assessment and Reporting of Tsunami) buoys in the open sea, who monitor the passing of tsunami waves at strategic locations and whose positions need to be optimised with respect to capital outlay and warning effectiveness. In the South China Sea, some individual buoys were deployed by China and Malaysia separately, no comprehensive warning system is currently in place. This study demonstrates the application of the warning potential method to optimise the locations of the DART buoys in designing an EWS in an attempt to mitigate the tsunami threat from the Manila Trench. It is found that people's reaction time plays a key role in the design of an EWS. Altering the reaction time of the population not only alters the proportion of the population that can be saved, but also the optimal buoy deployment and the optimal number of buoys deployed.
- Asia > China (1.00)
- Asia > Philippines > National Capital Region > City of Manila (0.25)
Abstract Where coastal tsunami hazard is governed by near-field sources, such as Submarine Mass Failures (SMFs) or meteo-tsunamis, tsunami propagation times may be too small for a detection based on deep or shallow water buoys. To offer sufficient warning time, it has been proposed to implement early warning systems relying on High Frequency (HF) radar remote sensing, that can provide a dense spatial coverage as far offshore as 200-300 km (e.g., for Diginext's Stradivarius radar). Shorebased HF radars have been used to measure nearshore currents (e.g., CODAR SeaSonde® system (), by inverting the Doppler spectral shifts, these cause on ocean waves at the Bragg frequency. Both modeling work and an analysis of radar data following the Tohoku 2011 tsunami, have shown that such radars could be used to detect tsunami-induced currents and issue tsunami warning. However, long wave physics is such that tsunami currents will only raise above noise and background currents (i.e., be at least 10-15 cm/s), and become detectable, in fairly shallow water, which would limit direct HF radar detection to nearshore areas, unless there is a very wide shelf. Here, we use numerical simulations of both tsunami propagation (in the Mediterranean basin) and HF radar remote sensing to develop and validate a new type of tsunami detection algorithm that does not have these limitations. This algorithm computes correlations of HF radar signals at two distant locations, shifted in time by the tsunami propagation time computed between these locations (easily obtained based on bathymetry). We show that this method allows detection of tsunami currents as low as 5 cm/s, i.e., in deeper water, beyond the shelf and further away from the coast, thus providing an earlier warning of tsunami arrival.
- Europe (0.88)
- North America > United States > Rhode Island (0.28)
- Asia > Japan > Tōhoku (0.25)
- Geophysics > Seismic Surveying (0.68)
- Geophysics > Electromagnetic Surveying (0.45)
Abstract This paper presents a time-domain decision support system based on deterministic, non-linear wave forecast and motion prediction for short-term offshore operations. The system consists of three individual constituents: sea state registrations, non-linear wave forecast and motion prediction. Surface elevation snapshots taken continuously by a ship board radar at great distance ahead the operational area are preprocessed by the wave monitoring system WaMoS II® 1 and used as input for the wave forecast tool. The non-linear wave propagation is modelled by applying the Higher Order Spectral Method (HOSM), which offers high accuracy and fast calculation time at once. The predicted surface elevation at the location of operation are used for the evaluation of the corresponding offshore structure response. For this purpose, Impulse Response Functions are implemented, which enable the fast determination of the response in time domain. The focus of the present study lies on the evaluation of the non-linear wave forecast and motion prediction part of the proposed decision support system. For illustrating the efficiency of the process, an offshore crane operation is investigated. The accuracy of the predicted (future) surface elevation as well as response of the multi-body problem is evaluated against model tests in the controlled environment of a seakeeping basin.
- Europe (1.00)
- North America > United States (0.94)
Abstract Extreme waves have caused a lot of ship accidents and casualties in ocean. So nonlinear dynamic strength of a containership in extreme wave is studied, the dynamic ultimate strength and deformational angle at midship are paid a close attention. On one hand, traditional ultimate strength evaluation is mainly carried out in quasi-static assumption and no dynamic wave effect is considered. On another hand, dynamic response of ship induced by wave is studied on the basis of hydroelasticity theory so that no nonlinear ship structural response can be obtained in large waves. Therefore, the 2D hydroelasto-plasticity method which takes a account of the coupling between time-domain wave and nonlinear ship beam is proposed. This method combines hydroelasticity method with FEM to calculate wave load and nonlinear dynamic structural responses in extreme wave. In addition, nonlinear dynamic FEM is also applied for the nonlinear dynamic strength of containership, the computational results of FEM including nonlinear VBM and deformational angle are compared with results of hydroelasto-plasticity and hydroelasticity. A number of numerical extreme wave models are selected for computations of hydroelasticityplasticity, hydroelasticity, and FEM. The difference between nonlinear VBM calculated by FEM and linear VBM calculated by hydroelasticity is observed and conclusions are drawn.
- North America > United States (0.28)
- Asia > China (0.28)
- Transportation > Marine (0.74)
- Transportation > Freight & Logistics Services > Shipping > Container Ship (0.59)
Influence of Joint Flexibility on Local Dynamics of a Jacket Support Structure
Popko, Wojciech (Fraunhofer Institute for Wind Energy and Energy System Technology IWES Northwest) | Georgiadou, Sofia (Norwegian University of Science and Technology) | Loukogeorgaki, Eva (Fraunhofer Institute for Wind Energy and Energy System Technology IWES Northwest) | Vorpahl, Fabian (Aristotle University of Thessaloniki)
Abstract The effect of different modeling techniques of the local joint flexibility on the local dynamics of a jacket support structure for an offshore wind turbine is investigated. Two numerical models of a jacket supporting a generic turbine are analyzed in the aero-hydro-servo-elastic tool ADCoSOffshore. The first model is setup with Euler-Bernoulli beam elements, while the second one utilizes superelements for the joints' representation and Euler-Bernoulli beams for the remaining parts of the structure. Time domain simulations are run for deterministic and stochastic load cases and local jacket dynamics are investigated. The local response of the braces is compared with the global response at the jacket legs in terms of power spectral densities. Damage equivalent loads are calculated at several positions along the jacket to capture the impact of local and global dynamics on those loads. It is observed that the superelement model leads in general to higher fatigue loads than the beam model. A methodology to remove the global motion component from the displacement time history of the brace central joint is discussed. Larger displacements of the brace central joints are observed for the superelement model than for the beam model. It is recommended to use superelement modeling technique for more a accurate representation of joints in the jacket support structures.
- Europe (1.00)
- North America > United States (0.68)
Abstract Steel catenary riser (SCR) has been widely used in deepwater oil and gas field development. A simple catenary shape is the most popular form of the SCR hanging off from a floating production system (FPS); and a lazy wave configuration is often considered when the riser experiences high fatigue effects associated with severe environmental conditions in the field. The design of deepwater risers depends on a large number of parameters, which may constantly change during execution of a project. It is always a great challenge for the riser design methodology to quickly and effectively accommodate these changes. Quick and correct responses to a design change are particularly critical for an on-going project, where concurrent engineering is of foremost concern. This paper presents a numerical method for simulating the deepwater SCR in-field profiles in simple catenary and/or lazy wave configurations. By using closed-form analytical formulations of various catenary shapes, the SCR can be described as a function of top tension and displacements at the hang-off point due to the floating production platform motions. The method is suitable for determining the relationships among riser properties, riser instant profiles, and the platform motions. The simulation quickly and correctly provides the hang-off loads at top, riser span variation and touch-down point (TDP) walking and curvature change, associated with the platform motions in the field. The results quantify the complex interplay among these key design variables, identify the controlling design variables, and allow the designer to improve and optimize riser system design.
- North America > United States (0.48)
- Asia (0.29)
These wave components must represent the total energy of the spectral model, This work describes a simplified analysis procedure, intended for and also the wave elevations and velocities observed in the actual preliminary design stages of risers connected to floating production irregular seastate. For this purpose, it is common to use at least 200 systems (FPS). The procedure may be seen as an extension of the regular wave components, or even more. Moreover, long simulation "equivalent regular wave" approach proposed in some design codes, times (typically 3 hours, or 10800s) are required to achieve statistical where the amplitude of a single regular wave (equivalent to a given stability of the random response to the irregular seastate, including for irregular seastate) is determined taking the motion RAO for a given instance the extreme values of platform motions, and riser top tensions. D.O.F. of the platform assumed to be the most critical for the riser response (usually the heave motions). Here, we consider an extension All those aforementioned factors may lead to excessive computational of this procedure where an ensemble of six regular waves is generated, times, and motivate the studies presented in this work, related to a one for each rigid-body D.O.F.. This wave ensemble could then be simplified representation of irregular seastates, adequate for employed for the dynamic analyses, allowing shorter simulation times preliminary design stages. For instance, in the context of the design (since the loading is deterministic), and leading to reasonable results methodology proposed by Girón et al. (2014), where thousands of with substantial reduction in CPU times. Case studies are presented to environmental loading cases should be employed in expedite analyses assess the proposed procedure, comparing its results with those intended to select critical cases, which should be subsequently verified provided by the full spectral irregular seastate approach.
Abstract Effects of phase transition of LNG during sloshing are investigated by numerically simulating LNG and its vapor as the approaching liquid inside tank. Boiling mechanism of liquid cargo in saturated state based on the basic theory of heat transfer is clarified with consideration of the LNG thermodynamic properties. And the effect of phase transition of cargo liquid during the sloshing is simulated using CFD code-Fluent. The parameter sensitivity analysis on LNG tank sloshing impact load is conducted based on the developed numerical method above. Liquid sloshing phenomenon inside tank is analyzed under the theoretical study and numerical method. The time histories of the liquid free surface shape and the dynamic sloshing impact inside the tank are obtained, which are well agreed with related data. The sloshing impact assessment method is developed through the parameter sensitivity analysis based on the numerical method.
- Energy > Oil & Gas > Midstream (1.00)
- Transportation > Freight & Logistics Services > Shipping > Tanker (0.52)
Abstract The objective of this paper is to present a methodology of unsteady CFD simulation of a floating offshore wind turbine (FOWT) experiencing platform motions. Based on the RANS equations and the SST α-ω turbulence model, aerodynamic simulations for a NREL 5MW turbine combined with OC3-Hywind spar buoy have been studied. The simulation results of a fixed wind turbine to verify the numerical model show relatively good agreement with NREL published data. Furthermore, based on the validation of three-dimensional CFD model the effect of typical periodic surge, pitch and yaw motions of the platform are investigated. With different periods and magnitudes of the platform motions, the aerodynamic performance of the wind turbine is demonstrated to vary dramatically. The power output performance of the turbine and the fatigue strength of structures could be significantly improved by reasonable controlling of the platform motions.
Abstract In this paper, the sediment-laden flow around a circular cylinder is numerically simulated in order to obtain better understanding of hydrodynamics associated. A range of cases with different Reynolds numbers (Re) are studies. The effects of the concentration of the sediment on the drag coefficient are investigated. Results show that due to the fact that the laden sand particle colliding the cylinder, it amplifies the drag coefficients, which increase as the increase of the sediment concentration, within the range of the application of the study. It is also observed that as the flow becomes more turbulent (higher Re), the effects of the laden particle on the drag coefficients become more significant.
- Asia > China (0.17)
- North America > United States (0.16)
- Research Report > New Finding (0.51)
- Research Report > Experimental Study (0.51)