Ahmad, Nadeem (Norwegian University of Science and Technology (NTNU)) | Bihs, Hans (Norwegian University of Science and Technology (NTNU)) | Chella, Mayilvahanan Alagan (Norwegian University of Science and Technology (NTNU)) | Kamath, Arun (Norwegian University of Science and Technology (NTNU)) | Arntsen, Øivind A. (Norwegian University of Science and Technology (NTNU))
Computational fluid dynamics (CFD) modeling of breaking waves over a slope and the resulting erosion in the case of an Arctic coastline is presented in this study. The study is performed with the open-source numerical model REEF3D. First, the numerical model is validated for the simulation of incident waves, wave breaking on a slope, and the sediment transport process. The numerical results show good agreement with wave theory and experimental data. The validated numerical model for the hydrodynamics and the sediment transport process is then used to simulate the coastal erosion process under the breaking wave impact on a vertical bluff. An Arctic coastline at Bjørndalen region at Isfjorden, Svalbard, is chosen, where a significant coastal erosion was observed during a storm event in September 2015.
Most of the Arctic coastline is susceptible to climate change. Because of global warming and the transfer of additional heat fluxes, the frozen period of the upper active layers in the Arctic coastline is reduced. Consequently, coastline stability decreases during the extended warmer period. The average thickness of the active sediment layer in Svalbard, Norway, varies between 1.0 and 10.0 m and consists of coarse-grained sandy soil (Fromreide, 2014). Climate change can affect this Arctic coastline in two ways. First, the extended warmer period results in the formation of deeper and weaker active sediment layers (IPCC, 2007). Second, the melting of the Arctic ice sheets increases the sea level, resulting in higher tides. In combination, the higher tides approach the Arctic coastline (Thompson et al., 2016) and erode the weaker active sediment layer. A recent example of this change has been experienced in the Bjørndalen region in Isfjorden, Svalbard, where significant coastal erosion occurred during a storm event in September 2015. The waves reached the cabins built near Isfjorden and resulted in an almost 1.0-m-deep scour hole (Barstein, 2015). Therefore, in order to better understand the coastal erosion phenomenon in the Arctic regions, the processes of wave breaking and the resulting sediment transport have to be investigated in detail. The study is also important for the design of new coastal structures and suitable mitigation measures at the Arctic coastline.
The manuscript presents initial results of a potential linkage between the mineral composition and structural strength in geological samples from a hydropower tunnel currently under construction. Changes in rock properties due to processes of both chemical as well as mechanical weathering are very important issues for water tunnels constructed for hydropower. Weathered and weak rock mass have strong slaking and deterioration potential if in contact with water, which may result failures in the unlined / shotcrete lined water tunnels. The slake durability of intact rock is in many cases closely linked to the mineralogy, especially on the content of weak clay minerals. When the weak rock mass is exposed to water it may lead to the degradation caused by the destruction of the intact rock structure. Such phenomenon may also aggravate swelling possibility in the rock mass if clay-bearing rocks are constituted by swelling minerals like montmorillonite (smectite).
The manuscript first evaluates the mineral composition of the rocks collected from the tunnel, and then the initial laboratory assessment on the extent of slaking is presented. Further, the slaking extent is linked to long-term stability issues in tunnels caused by slaking and disintegration.
From an engineering point of view, disintegration and swelling are among the most serious problems in underground rock excavation and are related to the alteration of previously competent rock mass (Wahlstr⊘m; 2012). Some rock types are especially prone to weakening and/or slaking when exposed to short term weathering processes of a wetting and drying cycles (ISRM 1977). As defined by Panthi (2006), slaking is the deterioration, weakening and breakdown of a rock material when subjected to cycles of drying and wetting. The phenomena is a result of shearing produced by volume change associated with wetting and drying, and is frequently observed in clay-bearing rocks as shales, mudstones and siltstones. In hydropower water tunnels, the rock mass is first exposed to a dry condition during construction due to contentious ventilation and use of heavy construction machinery and once construction is completed the tunnels are filled with water for very long period. Thus, knowledge of the interaction between rock mass and water saturation is crucial to prevent long-term failure or tunnel collapses.
This paper conducts a comparative evaluation of natural gas liquefaction processes developed for floating facilities. The simulation results are analyzed, mainly focusing on thermodynamic efficiency. The results are also compared with the AP-DMR process as a reference system, considering compactness, safety, and operational flexibility. The intended production capacity is 3 MTPA LNG.
The concept of floating LNG (FLNG) has attracted the attention of gas industry as natural gas demand is expected to grow (IGU, 2017). Deploying an FLNG vessel, however, has required the technical development of natural gas liquefaction processes to be suitable for the offshore environment. This has led many process suppliers and oil & gas operators to propose new liquefaction processes to be able to handle the harsh conditions.
Single mixed refrigerant (SMR) processes are one of the main suggestions for mid-scale FLNG, which is the range from 1.5 to 2 million ton per annum (MTPA) of LNG (Barclay and Denton, 2005; Meek et al., 2009). The small number of units and simple operation make SMR processes attractive to offshore applications in spite of a relatively low thermodynamic efficiency (Lee et al., 2012; Teles et al., 2010).
For a large production of LNG, in excess of 2-4 (MTPA), dual mixed refrigerant (DMR) processes have been recommended. DMR has a low specific power and a large train capacity compared to other LNG processes (Bukowski et al., 2013; Gilmour and Deveney, 2010). The mixed refrigerant (MR) for the pre-cooling cycle also gives better operational flexibility with the variation of feed gas conditions by changing the composition (Teles et al., 2010).
However, the large liquid inventory of hydrocarbons in SMR and DMR processes will increase the risk of fire and explosion on an FLNG vessel. Thus, gas expander based systems have been considered as an alternative process option for small-scale FLNG due to the inherent safety, simplicity, and ease of operation (Barclay and Denton, 2005; Foglietta, 2002b). However, the low thermodynamic efficiency and the small single train capacity make gas expander processes less favorable for floating LNG ships. To improve such low efficiency, a dual nitrogen expander cycle has been used (Dubar, 1997; Foglietta, 2002a). The efficiency was further increased by introducing an additional precooling cycle to a dual nitrogen expander process (Fredheim and Paurola, 2008).
Andersson, Leif Erik (Norwegian University of Science and Technology (NTNU)) | Scibilia, Francesco (Statoil Research Center and NTNU) | Copland, Luke (University of Ottawa) | Aftab, Muhammad Faisal (NTNU) | Imsland, Lars (NTNU)
In this study we show how to detect and extract the tidal and inertial oscillation from iceberg velocity data by using the multivariate empirical model decomposition. Due to the similar frequencies of both oscillations in regions subject to drifting icebergs, this is an extremely challenging filtering problem. The method is tested on two iceberg drift trajectories from the east coast of Canada, one at about 51°N and one at about 76.5°N. The two icebergs differ in latitudinal location, such that the inertial and tidal oscillations in the first data set have a slightly different frequency and in the other they are approximately the same. For the latter case a second filtering stage has to be included that uses tidal current information from a tidal current model. Finally we show how the multivariate empirical model decomposition can be used to analyze connections between current, wind and iceberg velocities. This information may help to improve either the ocean current and meteorological models or the iceberg drift model.
Icebergs provide a threat to marine navigation and offshore installations. A good operational iceberg drift forecast is therefore important for marine operations such as station keeping in regions subjected to drifting icebergs. A simplistic mechanistic dynamic iceberg drift model was developed in the 1980’s (Sodhi and El-Tahan, 1980) and further improved and tested by among others Mountain (1980); EI-Tahan et al. (1983); Smith (1993); Bigg et al. (1996); Eik (2009); Turnbull et al. (2015). An operational iceberg drift model was developed by the National Research Council of Canada and implemented at the Canadian Ice Service (CIS) and other agencies (Kubat et al., 2005).
However, large uncertainties in iceberg driving forces and in iceberg model parameters make the drift forecasting challenging. In fact, even the hindcasting of an iceberg drift trajectory with ocean currents, wind and waves measured in close proximity of the iceberg is difficult and not always successful (Smith, 1993; Andersson et al., 2017b).
Risers used for deep sea mining will be subjected to vortex-induced vibrations (VIV) caused by ocean currents. The internal flow, consisting of e.g. mineral ore and water, will have a non-uniform density. This traveling density wave may influence the dynamic response of the riser. In this paper, a simplified analytical approach is adopted to estimate the disturbance caused by the internal flow. The analytical model predicts a large disturbance (resonance) at a certain critical wavelength, which is verified by numerical simulations.
The global demand for minerals is continuously increasing. Higher living standard in developing countries is one important factor. In addition, various minerals are needed for the continued implementation of environmentally friendly technologies in developed countries. With this in mind, there is a growing concern about the scarcity of metals, as traditional land-based mines may be unable to meet future demands (Ali et al. 2017). As mineral resources on land are not evenly distributed, there may also be strategic reasons to why some nations want to find alternative sources.
Mineral deposits in the deep ocean include sea-floor massive sulfides (SMS) and manganese nodules. SMS deposits, found around the black smokers along the ridges of tectonic plates, are characterized by high grades of metals such as copper, zinc, silver and gold (Petersen et al. 2016). Manganese nodules are found on abyssal plains at great water depths, and contain manganese, nickel, cobalt and copper. Much research into deep sea mining was conducted in the 1970s (see e.g. Mustafa and Amann, 1980), but interest declined because of sufficient supply from mines on land. Recently, this interest has been renewed. Commercial deep sea mining is planned to commence outside the coast of Papua New Guinea in 2019 (Nautilus Minerals, 2016), and a mining pilot test was recently conducted close to Okinawa, Japan (METI, 2017).
Despite of large research efforts, many uncertainties remain. These are particularly related to environmental (Durden et al. 2017), but also economical and technical issues. As less than 0.5 % of the world's ocean area has been mapped (Beaulieu et al. 2017), much exploration is necessary before it is possible to quantify the amount of valuable minerals with certainty. Among the technical challenges are energy supply, extraction, vertical transportation and processing. When it comes to the transportation of mineral ore from seabed to surface, different methods have been suggested, such as mechanical lifting by a continuous bucket system, hydraulic lifting using slurry pumps and airlift methods (Schulte, 2013). In the case of slurry pumping or airlift, a vertical pipe, i.e. a riser, must be used to convey the ore/water mixture. As the riser represents a critical component of an ocean mining system, the integrity of this structure needs to be verified. The dynamic response of very long ocean mining pipes subjected to waves and top-end motion has been studied numerically by Chung and Cheng. (1996).
Torres, Cristian (Norwegian University of Science and Technology (NTNU)) | Kappes, Mariano (Comisión Nacional de Energía Atómica) | Johnsen, Roy (Norwegian University of Science and Technology (NTNU)) | Iannuzzi, Mariano (Curtin University)
Super duplex stainless steels are ferritic-austenitic stainless steels with 25 wt% Cr and a pitting resistance equivalent (PRE) ≥ 40. Even though other elements, such as Cr and Mo, have been studied in much more detail than W, research has shown that an optimal composition exists, in which W in solid solution improves localized corrosion resistance. Outside this range, W is ineffective or even detrimental. However, the mechanisms by which W improves localized corrosion resistance in stainless steels are unclear. For example, debate still exists as to whether W enhances passivity or facilitates repassivation.
In this work, two super duplex stainless steels were investigated: a W-free (UNS S32750) and a 2.1 wt% W-containing (UNS S39274) grade. The first goal was to study differences in the overall localized corrosion resistance; while the second objective was to gain an insight into the mechanisms by which W affects the localized corrosion performance of super duplex stainless steels. The work was divided into two parts. Firstly, anodic potentiodynamic polarization curves were conducted in different simulated pit environments at various temperatures. Two simulated pit solutions were tested: 1 M HCl and 7 M LiCl adjusted to a pH of 0. In the second part, crevice repassivation potentials were measured using the potentiodynamic-galvanostatic-potentiodynamic technique in 3.5 wt% NaCl pH = 6.5 solution. This investigation will provide evidence regarding the influence of W in passive film stability and repassivation kinetics
Super duplex stainless steels (SDSS) are a type of highly alloyed stainless steels, with at least 25 wt% Cr. Additionally, SDSS have a dual austenitic and ferritic microstructure, with an ideal ratio between phases as close to one as possible.1 Because of their high Cr, Mo, and N content, SDSS are widely used in corrosive environments where high corrosion resistance is required. However, SDSS can suffer localized corrosion in seawater and are limited to a maximum service temperature of 20°C according to NORSOK M-0012 and ISO 214573.
Alteskjær, Sverre A. (Sintef Ocean AS (MARINTEK)) | Lindstad, H. Elizabeth (Sintef Ocean AS (MARINTEK)) | Sandaas, Inge (Naval Architect) | Solheim, Astrid (Norwegian University of Science and Technology (NTNU)) | Vigsnes, Joakim T. (Norwegian University of Science and Technology (NTNU))
The development of Open hatch carriers (OHC) dates back to the early 1960s linked to transport of newsprint from the paper mills along the coast of British Columbia (Canada) to the news-printers in San Francisco and Los Angles (USA). Prior to that, conventional general cargo ships, tween-deck liners and trampers transported newsprint and lumber (timber). This implies that the present OHC fleet are competing with dry bulkers for typical dry bulk cargoes, and with container vessels and Ro-Ro's for cargo types, which requires more careful handling. The paper presents an overview of the historic development of transport efficiencies from the steam ships used in newsprint and timber trades in the early 1900 up to the latest generation of OHC's. The results indicates that alternative combinations of main measurements to enable lower block coefficients reduces fuel consumption and greenhouse gas emissions (GHG) per freight unit transported. Moreover, these designs might increase the competitiveness of Open Hatch vessels versus their competitors, i.e. dry-bulk, container and Ro-Ro. From the first days of human civilization, sea transport has dominated trades between cities, nations, regions, and continents.
We develop a general framework for computing reflection traveltime derivatives with respect to offset in layered anisotropic media with weak lateral heterogeneities from curved interfaces and smoothly variable velocities. We specify the expression for the second-order derivative related to normal moveout (NMO) velocity and show that it is influenced by both types of heterogeneities. In general layered media, the effects get accumulated along the raypath from the source to the receiver and can be computed using the proposed recursive relationship. Numerical examples show that taking into account heterogeneities can lead to more accurate moveout approximations and therefore, aid in analysis of estimated NMO velocities in practice.
Presentation Date: Monday, September 25, 2017
Start Time: 2:40 PM
Location: Exhibit Hall C/D
Presentation Type: POSTER
Vucelic, Lara Antonia Blazevic (Norwegian University of Science and Technology (NTNU)) | Duffaut, Kenneth (Norwegian University of Science and Technology (NTNU)) | Avseth, Per (Norwegian University of Science and Technology (NTNU))
These processes are affected by rock microstructure, pressure regimes and temperature history. Data from 30 wells have been used to investigate and compare the changes in porosity, bulk density, elastic moduli and wave propagation velocities between mid-Jurassic sandstones in the North Sea and the Norwegian Sea. Mechanical compaction and quartz cementation models are used together with rock physics diagnostics to describe these changes. Introduction The physical properties of rocks are fundamental for the study of sedimentary basins and the characterization of hydrocarbon reservoirs. Properties such as porosity, bulk density and wave propagation velocities of the rock can be obtained or derived from well log data and they may provide information about rock composition and structure.
Xing, Liyuan (Norwegian University of Science and Technology (NTNU)) | Aarre, Victor (Schlumberger AS) | Barnes, Arthur (Pagosa Geophysical Research) | Theoharis, Theoharis (Norwegian University of Science and Technology (NTNU)) | Salman, Nader (Schlumberger AS) | Tjåland, Egil (Norwegian University of Science and Technology (NTNU))
Instantaneous frequency is widely used for identifying specific seismic events, such as abnormal attenuation and thin bed tuning, based on its frequency content. It is one of the important seismic attributes related to the complex seismic trace. Although the definition itself is clear in theory, in practice the calculation can vary considerably, and deviate from the theoretical aim. Despite several decades since it occurred, there is still little consistency in the calculations of instantaneous frequency. We thus propose a robust and reliable scientific process to objectively compare various implementations of instantaneous frequency. To this end, through theory deduction and a physical model illustration, a complicated synthetic test dataset based on two oscillating function combinations, with varying frequencies and amplitudes, is generated. Correspondingly, its ‘ground truth’ instantaneous frequency is calculated by the analytic formula. In addition, several issues and weaknesses of current instantaneous frequency computations are pointed out and are considered in proposed quality metrics. Preliminary tests with quantitative and qualitative results show the effectiveness of the synthesized dataset and quality metrics for instantaneous frequency evaluations. Thereby, the benchmarking process may eventually improve the quality of instantaneous frequency algorithms throughout the industry.
Presentation Date: Wednesday, September 27, 2017
Start Time: 2:15 PM
Presentation Type: ORAL