Sfouni-Grigoriadou, Mariangela (University of Louvain-la-Neuve) | Delnooz, Pierre (Fugro GeoConsulting) | Guilmot, Matthieu (University of Louvain-la-Neuve) | Ingarfield, Samuel (University of Louvain-la-Neuve) | Spinewine, Benoit (Fugro AG,)
In the present work, a two-layer model is introduced to study the dynamics of transitional flows. It considers a dense basal layer with high density that is characterized by a non-Newtonian rheology, and a dilute upper layer of variable density constituting a turbulent turbidity current with Newtonian rheology. Results from this depth-averaged two-layer model are presented for a 2D case on idealized bathymetry featuring a slope break, as well as for a hypothetical 2D case study on an actual submarine bathymetry.
The gradual depletion of nearshore resources and rapid technological advances in oil and gas production have forced the industry to develop fields often located beyond the continental shelf, in deep water environments susceptible to mass movement events. The risk to subsea infrastructure from these events is often assessed through an examination of the potential instability of nearby slopes, followed by numerical modelling of potential slide runout behavior.
As they run down the slopes and interact with the sea floor and ambient sea water, these mass movement events may evolve from a dense, debris flow to a dilute, turbidity current. According to Locat and Lee (2005), the release and development of a slide can be divided into three main phases: (i) the initial failure and break-up of blocks and slumps, (ii) the transformation of the released material to a viscoplastic fluid and the development of a debris flow and (iii) the generation of the turbidity current due to the shear stress on top of the debris flow producing a cloud of suspended matter.
Subaqueous cohesive debris flows are dense, viscous sediment-water mixtures where the wet clay forms a mud-matrix that supports coarsergrained material as flow moves. Turbidity currents are particle-laden flows with volumetric concentration generally below 10%, where the particles are kept in suspension through turbulent mixing (Middleton and Hampton, 1976).
Laboratory experiments were undertaken by Felix and Peakall (2006) to investigate the transformation mechanisms of debris flows into turbidity currents. The transformation includes multiple processes like erosion off the dense mass, breaking apart of the dense underflow, breaking of internal waves and turbulent mixing. Some of these processes take place simultaneously in a flow event, while other at different places and positions. It was observed that more transformation to a turbidity current layer occurs for less-cohesive debris flows.
Suspended sediment concentration (SSC) environment is analyzed based on the observed data during the period from 1985 to 1995, Jan. 2006, Jun. 2009 and Aug. 2009 and the remote sensing data from 1987 to 2005. Results from the study suggest that: (1)SSC has obvious seasonal, temporal and spatial change, which is controlled by tidal range; (2) SSC during the strong wind is 3-5 times the general weather, and the SSC peak has certain hysteresis with wave height peak; (3) in most cases, waves are the main power of sediment movement in the nearshore shallow waters, sediment movement by wave and tidal current plays an important influence on the Haizhou Bay terrain evolution.
SSC is an important indicator to reflect the sediment transport and resuspension processes, which are the important factors to study the condition of an estuary, its navigation environment and harbor construction (Zuo et al., 2012). SSC of the estuary or bay is controlled by multiple factors including freshwater and sediment discharges of the river, tides and waves (Li et al., 2010). Change of SSC can indicate the changes of sediment sources and transport processes or dynamic conditions.
Haizhou Bay is an open bay on the verge of Yellow Sea. Port development is still a blank in the bay at present. In order to develop the port resources of Haizhou Bay and the economic development of Jiangsu Province, Ganyu Harbor District of Lianyungang Port will be planned in northern sea area of Haizhou Bay, which is the adjacent area of Shandong Province and Jiangsu Province. In recent years, relative research achievements (i.e. geomorphic features, shoreline change, hydrodynamic and sediment) become abundant in response to the construction of Ganyu Harbor District (Fan et al., 1997; Sun et al., 2003; Zhao et al., 2008; Zhang et al., 2008). However, the characteristics of SSC distribution study of Haizhou Bay are rare.
The aim of this study is to contribute to understanding of the effects of submarine mass movement, ‘sliding block’, on tsunami amplitudes using basic source model. This study aims to see effect of movement as a block differently from pioneering studies that investigate submarine landslide and its effects on tsunami amplitudes. To define model, two sliding blocks moving with different velocities in different directions are considered. The differences of tsunami peak amplitudes among the sliding blocks’ movements in different depths and distances are compared. The interaction of near fiel tsunami amplitudes are discussed with different velocities, depths and distances. In the model, mass is conserved. Laplace and Fourier transform methods are used for the solution of equations and linearized shallow water wave theory is assumed.. The results show that during the source process, when the velocity of masses are much faster than velocity tsunami, the displacements on the free surface above the source resembles the displacement of the floor. Results for tsunami peak amplitudes are presented for mentioned parameters. The effects of sliding block slide as a kind of submarine mass movements on the tsunami amplitudes and the interaction of the tsunami wave forms are examined for specified parameters and illustrated.
Tsunami is one of the big disasters in the world. It can be generally created by the vertical motion of a fault under the sea bottom during the earthquake, submarine volcanic eruption, atmospheric conditions, submarine slides and slumps (Gutenberg, 1939). This gravity waves with long periods may have destructive effects along the shore. Due to this, it is important to recognize this disaster very well. Based on this necessity, many studies have investigated about tsunami models for years. Pioneering studies are especially about submarine slides-slumps and variable parameters that affect the tsunami amplitudes. This study is also an opportunity to see the similarities and differences between slides and sliding blocks. The ‘block slide’ could be used to represent the motion of the collapsed blocks at the Blake Escarpment, east of Florida. In this area, ‘’deep sea floor has enormous agglomeration of blocks, commonly 10 km across, that appear to have fallen from the face of the cliff’’ (Dillon et al.,1993). Other examples are the block slide at the base of Middle Canyon along the Beringian Margin in Alaska (Carlson et al.,1993) and the Sur submarine landslide, where ‘’intact sections of slope sediment as large as office buildings (≤ 25 m high) moved 5 km down the continental slope and as much as 20 km the gentle 0.5° incline of Monterey fan. Smaller, house-sized (≤ 10 m high) blocks were transported as 30 km further’’ (Gutmacher and normark, 1993). To define model, two sliding blocks moving with different velocities in different directions are considered in this study. The differences of tsunami peak amplitudes among the sliding blocks’ movements in different depths and distances are compared. As the velocity of tsunami wave is equal to square root of gravitational acceleration and the ocean depth, the depth effect on tsunami amplitude observed.
The wave environment in the Barents Sea is presented in this paper using wave hindcast data for a period of 57 years for one location. It was found that swell is dominant at this location most of the time in the winter season, and that swell contributes significantly to the wave environment at the location in the summer season. This study shows that a double peak spectrum may be more suitable to characterize most operational sea states in the Barents Sea. An illustration is shown on how the suitable wave spectrum is used in short-term analysis of a vessel response.
For design purposes, the wave environment may be described by a deterministic design wave method or a stochastic design wave method, depending on the type of response problem under consideration. However, for weather restricted marine operations, the wave environment should be described by the stochastic design wave method (DNV, 2011). More generally, the stochastic design wave method is suitable for linear response problems, for instance, for estimating the wave frequency responses of vessels or floating platforms. For linear response problems, the analysis can be conveniently carried out in the frequency domain. Such an analysis requires a suitable wave spectrum, and a transfer function describing the response properties of the vessel or floating platform.
The measured wave spectrum at a location represents a description of the distribution of wave energy among different wave frequencies of wavelengths for a sea state, and is seldom available. One is therefore often left with the choice of selecting among the available theoretical wave spectrum models. The commonly used wave spectra on the Norwegian continental shelf (NCS) are the Pierson-Moskowitz (PM) spectrum, the JONSWAP spectrum, and the Torsethaugen spectrum.
This paper gives the description of the wave environment in the Barents Sea, using wave hindcast data from the Norwegian Reanalysis 10 km (NORA10) database. NORA10 is a combined high-resolution atmospheric downscaling and wave hindcast based on the European Reanalysis dataset (ERA-40) (Reistad et al., 2011). NORA10 produces 3-hourly wave fields at a resolution of 10 km. The NORA10 database used in this study covers a period of 57 years (September 1957 - June 2014), and comprises 166053 number of wave data. The study considered wave hindcast data from only one location, and the coordinates of the location are 72.02°N 22.10°E, a map showing the location is presented in Fig. 1.
A new model is established to estimate the reaction forces and torques on cutter head of cutter suction dredger in rock dredging. In our model, the cutting parameters of the teeth on cutter head are determined by numerically simulating the relative positions between the teeth and rocks, then those parameters are used for calculating the forces on the teeth. Summing up all the forces on all the teeth and the moments of all the teeth around the axis of the cutter head, the reaction forces and torques on cutter head can be obtained. The proposed model is effective for estimating dredging loads.
Cutter suction dredger is a highly efficient and core piece of dredging equipment, which is widely used in the waterway dredging, port construction, and reclamation and other projects. The loads on the cutter head have great effects on the design of bridge structure and mooring of the ship, because the loads are transferred to the ship body through the bridge and are resisted by the loads on the mooring system. It is essential for the accurate calculation of the dredging loads that are imparted onto the bridge structure while dredging for safety. Pan (Pan, Yang and Tang, 2009) and Yang (Yang, Zhu, Fan and Pei, 2012) analyzed the dynamic loads on the cutter head in dredging sediment based on two-dimensional cutting theory. Li (Li, Jiao, Huang, Jia, Wei, Liu, Ai and Lu, 2013) simulated the sediment dredging process of the cutter suction dredger. With the development of dredging industry, the cutter suction dredgers are now used for dredging soft rock or hard rock rather than just for sediment or soil. Gao (Gao, 2007) introduced the technicals related to the rock dredging with cutter suction dredger. Yao (Yao, 2011, Yao and Yang, 2011) and Chen(Chen, 2012, Chen and Yang, 2013) investigated the methods to estimate the dredging loads of the large cutter suction dredger with the theory from coal mining. Ma (Ma, 2015, Ma, Ouyang, Yang and Liu, 2014) built a model to estimate the dynamic loads on cutter heads. In Ma’s model, the two-dimensional rock cutting theory was used to calculate the cutting forces, and the effects of some dredging parameters were investigated. However, in all of the models for estimating the dredging loads, the effects of the breakout angle on the cutting forces for rock cutting have not been considered except two-dimensionally, which can result in underestimating the fluctuation of the dredging loads.
The aerodynamic performance of the floating offshore wind turbine has an extra level of complexity than that of bottom-fixed wind turbines because of the motions of the supporting platform. In this paper, the unsteady aerodynamic performance of the NREL-5MW Baseline wind turbine with periodical surge and pitch motions of its supporting platform are investigated. The three-dimensional Reynolds Averaged Navier-Stokes equations are solved for the aerodynamic numerical simulation. The naoe-FOAM-os-SJTU solver, which is based on OpenFOAM and overset grid technology and developed for ship and ocean engineering problems, is employed. From the simulation, the time series of the unsteady torque and thrust are obtained, together with the detailed information of the wake flow field, and the pressure coefficient distribution in different cross-section are also available to clarity the detailed flow filed information. The simulation results are compared both with those obtained from aerodynamic simulation of wind turbine without effects of platform motions, and with other approaches in previous studies. The simulation results show that the pitch motion has more significant effects on the aerodynamic forces and moments of the rotor than the surge motion does. And the motion of the platform especially the pitch motion may bring very bad influence on the turbine forces and wake flow, even on the power generation in case of very severe pitch motion.
As renewable and sustainable, wind energy represents a potential to solve the energy and environment crisis, especially for the coastal countries which have enormous ocean wind energy resource. With special and strong advantages over onshore or fixed-bottom offshore wind turbines, floating offshore wind turbines (FOWT) become more and more competitive. But environment loads on FOWTs have an extra level of complexity, among which the aerodynamic loads are of great significance.
Since the onshore wind turbines were widely used much earlier, there exist many kinds of methods for the aerodynamic simulation of a wind turbine. The three main method for the aerodynamic performance simulation of the wind turbines, which are the Blade Element Momentum theory (BEM), the Generalized Dynamic Wake model (GDW) and the Computational Fluid Dynamics (CFD), are well developed for the steady aerodynamic simulation of the fixed-bottom wind turbine, among which BEM and CFD are also developed for unsteady simulations.
Raptodimos, Yiannis (University of Strathclyde) | Lazakis, Iraklis (University of Strathclyde) | Theotokatos, Gerasimos (University of Strathclyde) | Salinas, Raul (University of Strathclyde) | Moreno, Alfonso (University of Strathclyde)
This paper presents the onboard measurement campaign for the case study of a container ship and provides a customary methodology for monitoring important machinery systems. The main principle aim of this paper is to collect important machinery data and parameters from critical systems, located in the engine room of the ship, by determining systems to be monitored, scenarios for monitoring, sensors and suitable portable equipment and physical parameters to be inspected.
Maintenance is an important contributor to reach the intended life-time of technical capital assets and is defined as a combination of all the technical and associated administrative activities required to keep equipment, installations and other physical assets in the desired operating condition or to restore them to this condition (BS, 1993). Maintenance also includes the engineering decisions and associated actions that are required for the optimisation of specified equipment capability, meaning the ability to perform a specified function within a range of performance levels that may relate to capacity, rate, quality, safety and responsiveness. Furthermore, maintenance costs are a significant portion of the operational cost and breakdowns and downtime have an impact on plant capacity, product quality and cost of production as well as on health, safety and the environment. Thus, nowadays, the shift of maintenance as a strategic perspective within a company organization can be attributed to the utilisation of more advanced technologies, increased emphasis on safety, new environmental legislations, optimised operations with increased fuel efficiency and reduction of emissions (Parida et al., 2015) .
This paper presents the results of an experimental study to investigate the effects of fines content and fines type on the liquefaction resistance. Clean sands were mixed with various amounts of two type fines (nonplastic fines FC200 and low plastic fines FC400). The cyclic triaxial tests were performed on the samples of clean sand and sand-fines mixtures. The liquefaction resistance, in terms of CSR at 15 cycles, increased 4.8-9.2% as the various fines content in the sand with low plastic fines (FC400) mixtures, but decreased 6.0-18.4% as the various fines content in the sand with nonplastic fines (FC200) mixtures.
Field investigation of liquefaction damage areas (Bray et al. 2004; Chu et al. 2004) after the 1999 Kocaeli, Turkey and Chi-Chi, Taiwan earthquakes revealed that in many liquefaction sites, the fines content (FC) of the soil was as high as 45% or more. The boundary curves in the simplified procedure pioneered by Seed and Idriss (1971), and updated in Seed et al. (1985) and Youd et al. (2001), were prepared only for three classes, those with FC ≤ 5%, 5% < FC < 35%, and FC ≥ 35%, indicating that there was a lack of field liquefaction data with FC > 35%. The observation of soil liquefaction performance in the Kocaeli and Chi-Chi earthquakes suggested that the effect of high fines content on the liquefaction resistance need further study.
In recent years, results of many studies on the effect of fines content have been reported. However, there appears to be some confusion as to whether the liquefaction resistance of soils would increase or decrease with the increase in fines content. Some studies indicate that the presence of fines increases liquefaction resistance (Seed, 1987; Youd et al., 2001; Idriss and Boulanger, 2015), while others suggest that increasing fines content (FC) decreases liquefaction resistance (Kokusho et al., 2012; Chen et al., 2014). Besides, the other types of fines effects have been reported. Liquefaction resistance decreased initially with the increase in fines content and then increased as fines content continued to increase (Polito and Martin, 2001; Baziar and Sharafi, 2011; Karim and Alam, 2014). Possible reasons for such discrepancy include: difference in experimental parameters, type of fine grained material used, plasticity of the soil, and range of fines content used in the experiments.
Hu, Hsuan-Teh (National Cheng Kung University) | Yang, Chi (National Cheng Kung University) | Yeh, Ding-Sheng (National Cheng Kung University) | Liaw, Shyne-Ruey (CECI Engineering Consultants, Inc.) | Lin, Chu-Kuan (CECI Engineering Consultants, Inc.) | Liu, Yu-Ming (CECI Engineering Consultants, Inc.)
In recent years, nations over the world were looking for alternative energy sources to reduce global warming caused by traditional fossil fuel burning. Renewable energy sources like wind power have great opportunities in this direction, because of low pollution. The offshore wind turbine (OWT) structures are frequently subjected to dynamic loads during operation. Hence, knowledge of their dynamic characteristics such as their natural frequencies, is essential to avoid damaging resonances.
In this study, the Abaqus finite element program is used to calculate the natural frequency of a jacket-type offshore wind turbine supporting structure. During the analysis, the nonlinear behavior has also been considered. Four models: the finite element model, the hybrid finite-infinite element model with the soil material simulated by infinite element, the soil spring model adopting the soil equation proposed by the American Petroleum Institute, and the equivalent soil spring model were utilized in this study. The nonlinear behavior of the soil-pile interaction and the natural frequency of the OWT structure were thoroughly analyzed.
Many offshore wind turbines use the jacket foundation for a costeffective design. With the small area and high stiffness of the tubular members, the stability and the resistance of the structure to withstand the environmental load is higher than those of other types of foundations. Many other types of foundations such as gravity, monopiles, and tripods, are also used as the support of offshore wind turbine structures (Kaiser and Snyder, 2012). During the design of the structure, it's essential to correctly estimate the natural frequency to prevent resonances causing damage to the offshore wind turbine (OWT) structure.
In the analysis of the static and dynamic response of offshore wind turbine structures, the soil-pile interaction plays a significant role. Poulos (1971) proposed an elastic solution for the horizontal displacement and rotation of a single pile subjected to lateral loading and moment. Further research focused on the nonlinear behavior of the soil-pile interaction, which may be described as a mathematical function of soil and pile properties. Several researches used the p – y curve method to investigate the nonlinear behavior of different soil types. O’Neill and Murchinson (1983) developed the p – y curves for sand, while Dunnavant and O’Neil proposed a p-y curve for clay. Many results of these researches were adopted by the API standard (2000), which serves as the basis for many designs of OWT structures. Mitwally and Novak (1987) used linear analysis to depict the pile–soil interaction regarding the response of an offshore tower to wave loading. Chaudhry (1994) used finite element method and boundary element method to investigate the pile-soil interaction with single and multiple piles in offshore, and determined the ultimate lateral soil reaction. Another method for soil-pile interaction analysis is the finite/infinite element method. The use of the infinite element method on semiinfinite domains can prevent the reflection of energy from the boundary to the domain of interest. Medina (1992) presented a dynamic soilstructure interaction for homogeneous and layered soil using infinite element method.
Panapakidis, Ioannis P. (Technological Education Institute of Thessaly Larisa) | Michailides, Constantine (Aristotle University of Thessaloniki (A.U.Th.)) | Angelides, Demos C. (Norwegian University of Science and Technology)
This paper addresses two objectives for the case of missing wind speed data: (i) the implementation of clustering techniques for completion of missing wind speed data and (ii) the development of offshore wind speed forecasting models. Various clustering algorithms are compared in terms of better portioning of the wind speed data. With the aid of a robust clustering tool, a more in depth analysis can be held on wind speed data drawing useful conclusions about the data structure. In addition, three novel techniques are developed for the completion of the missing data. Furthermore, two commonly used forecasting models are used, namely a Feed-Forward Neural Network (FFNN) and the Adaptive Neuro-Fuzzy Inference System (ANFIS). The purpose is to train and test these models under the limitation imposed by the incomplete data set. The present paper serves as a necessary step in the problem of handling incomplete wind speed data towards the assessment of offshore wind energy potential.
Fixed bottom Offshore Wind Turbines (OWTs) are considered as an efficient solution to cope with the increasing demand in power grids globally. OWTs have been passed successfully into the phase of commercialization and industrialization and there is an increasing trend for using this very promising renewable energy technology and its products widely in the coming years.
During the last years an increasing number of research efforts and pilot programs brought forth the benefits provided by OWTs both for utilities, grid operators, self-producers and societies. OWT is a contemporary topic that is becoming the focus of interest of the research community. In June 2015 3,072 fully grid connected offshore wind turbines existed in 82 wind farms across 11 European Union (EU) countries, with a capacity of 10,393.6 MW. The average water depth of these OWTs is equal to 22.4 m. Around 90% of the already installed OWTs are supported in monopile fixed bottom substructure foundation type. The coming years is expected that OWTs will dominate in renewable energy sector globally. Nowadays, the installed offshore wind capacity is growing with a rate of 40% per year.