Morita, Hiromitsu (National Institute of Advanced Industrial Science and Technology (AIST)) | Muraoka, Michihiro (National Institute of Advanced Industrial Science and Technology (AIST)) | Yamamoto, Yoshitaka (National Institute of Advanced Industrial Science and Technology (AIST))
This paper measures the thermophysical properties of natural methane hydrate (MH)-bearing sediments recovered from the Nankai Trough, Japan. The thermal conductivity, thermal diffusivity, and specific heat of the sample under vertical stress (VS) loading were measured by the hot-disk transient method. The thermal conductivity of the sediments increased with increasing VS. The specific heat and thermal diffusivity have a constant value independent of VS. After MH dissociation, the thermal conductivity and the specific heat dropped significantly, and the thermal diffusivity was increased. In addition, the thermal conductivity, specific heat, and thermal diffusivity were calculated by an estimation model.
Methane hydrate (MH) is expected to be developed as an unconventional natural gas source, replacing existing fossil fuels. MH is a crystalline solid in which cages of hydrogen-bonded water molecules enclose the methane gas molecules. MH is stable in a high-pressure/low-temperature environment. A large amount of MH is known to exist in permafrost on land and in sedimentary layers beneath the seabed (Sloan and Koh, 2007).
The collected seismic data for oil and gas exploration show a wide distribution of bottom-simulating reflections (BSRs) under the seafloor in the Nankai Trough region near the Japan Sea coast. BSRs indicate the lower limit of gas hydrate stability zone in a vertical profile. In 1999, the first Nankai Trough methane hydrate exploration well was drilled. In early 2004, the Japan Ministry of Economy, Trade, and Industry drilled a multiwell from Tokaioki to Kumano-nada (Tsuji et al., 2009). The core was recovered using a pressure-temperature core sampler, which maintained the in-situ condition of 16 excavation sites at water depths ranging from 720 to 2,030 m in the same year. Recovered core analysis confirmed that the MH-bearing sediments in the Nankai Trough area are pore-filling-type hydrates (Fujii, Nakamizu, et al., 2009; Fujii, Saeki, et al., 2009).
Kim, Taeyoung (Ship and Offshore Research Center, Samsung Heavy Industries) | Yoo, Seonoh (Ship and Offshore Research Center, Samsung Heavy Industries) | Oh, Semyun (Ship and Offshore Research Center, Samsung Heavy Industries) | Kim, Hyun Joe (Ship and Offshore Research Center, Samsung Heavy Industries) | Lee, Dongyeon (Ship and Offshore Research Center, Samsung Heavy Industries) | Kim, Booki (Ship and Offshore Research Center, Samsung Heavy Industries)
Reduction of fuel oil consumption in sailing vessels has been of great interest even with the recent trend of moderate oil prices. The added resistance contributes to the increase in fuel oil consumption of vessels in the actual sea environment. Therefore, the precise prediction of the added resistance is of great importance for developing highly energy efficient vessels. In this paper, the numerical and experimental studies are performed to estimate the added resistance of a liquefied natural gas (LNG) carrier. A series of self-propulsion tests are carried out for validation purposes. The linear potential flow method and fully nonlinear Reynolds-averaged Navier-Stokes analysis are employed for numerical evaluation of added resistance in waves. The transfer functions of the added resistance from the three different approaches are compared, and noticeably different results are observed, especially around the short wave region. The discrepancy is then analyzed systematically by comparing the local waves at different positions along the vessel. A comparison of the numerical and experimental results is summarized, and the validity of each approach is then discussed.
Recently, the added resistance in waves is of great concern because of the growing demand of an optimized ship hull for energy-saving efficiency in an operational sea environment. A fundamental step in the optimization is to estimate the vessel’s added resistance in an appropriate manner. Theoretical and experimental studies have been devoted to the added resistance, and the efforts in improving the accuracy of estimation have been constantly made.
Chen, Yung-Wei (National Taiwan Ocean University) | Shih, Chao-Feng (National Taiwan Ocean University) | Liu, Yu-Chen (National Taiwan Ocean University) | Soon, Shih-Ping (National Taiwan Ocean University)
This paper presents an equal-norm multiple-scale Trefftz method (MSTM) associated with the group-preserving schemes (GPS) to tackle some difficulties in nonlinear sloshing behaviors. The MSTM combined with the vector regularization method is first adopted to eliminate the higher-order numerical oscillation phenomena and noisy dissipation in the boundary value problem. Then, the weighting factors of initial and boundary value problems are introduced into the linear system to prevent the elevation from vanishing without iterative computational controlled volume. More important, the explicit scheme, based on the GL (n, R), and the implicit scheme can be combined to reduce iteration number and increase computational efficiency. A comparison of the results shows that the proposed approach is better than previously reported methods.
Sloshing of liquid in tanks has received considerable attention from many researchers in related engineering fields. The problem arises because excessive sloshing of the confined liquid can strongly damage the structure or the loads induced by sloshing, which may seriously modify the dynamics of the vehicle that supports the tanks—for example, fuel sloshing in liquid propellant launch vehicles (Lu et al., 2015), oil oscillations in large storage tanks as a result of long-period strong ground motions (Hashimoto et al., 2017), and sloshing in nuclear fuel pools owing to earthquakes (Eswaran and Reddy, 2016). Besides, sloshing effects in the ballast tanks of a ship may cause it to experience large rolling moments and eventually capsize because of loss of dynamic stability (Krata, 2013; Sanapala et al., 2018). Also, if the forcing frequency coincides with the natural sloshing frequency, the high dynamic pressures, by reason of resonance, may damage the tank walls. Thus, accurate prediction of sloshing behaviors in tanks driven by external forces is very critical for successful structural design and reducing impacts on vehicle maneuvering.
Müller, Nathalie (Fraunhofer-Institut für Windenergie und Energiesystemtechnik (IWES)) | Kraemer, Peter (University of Siegen) | Leduc, Dominique (Research Institute of Civil Engineering and Mechanics (GeM)) | Schoefs, Franck (Research Institute of Civil Engineering and Mechanics (GeM))
A fatigue test has been conducted on a large-scale offshore wind turbine grouted connection specimen at the Leibniz University of Hannover. For detecting damages in the grouted joint, a structural health monitoring (SHM) system based on fiber optic sensor-type fiber Bragg grating (FBG) has been implemented. By extracting the features of the FBG signal responses using the Wigner–Ville distribution (WVD) and one of its marginal properties, the energy spectral density (ESD), it is possible to detect the occurrence and the global severity of the damage. Some information about the local severity of the damage has also been obtained.
The grouted connection consists of the high-performance grout-filled space between the two structural steel components of respectively the sleeve and the pile of offshore wind turbines (OWTs). For monopile OWTs, it is located around the water level between the transition piece and the pile, whereas for jacket and tripod OWTs, it is located just above the seabed, between substructure and foundation pile. While grouted joints for monopiles are exposed to bending moments, grouted joints for latticed substructures (tripods and jackets) are exposed to predominant axial loadings and low torsional moments (Schaumann and Böker, 2005; Schaumann, Lochte-Holtgreven et al., 2010). It is a critical structural part of OWTs. In 2009–2010, engineers reported grouted connection failures causing slight and progressive settlement of turbines. The problem affected approximately 600 of the 988 monopile wind turbines in the North Sea, requiring further investigations concerning the design of the grouted connection (Rajgor, 2012). Since then, two grouted connection designs reducing the axial forces in this area have been recommended by Det Norske Veritas (2014): using a conical grouted connection (first design) or a tubular connection with shear keys (second design).
Gong, Yufeng (China Ship Development and Design Center) | Peng, Weicai (China Ship Development and Design Center) | Zhang, Junjie (China Ship Development and Design Center) | Liu, Jingxi (Huazhong University of Science and Technology (HUST))
Stiffened plate is a fundamental element of ship and other engineering structures. Deflection and fracture of a clamped stiffened plate under lateral indentation by a spherical indenter was investigated by a semi-analytical approach and experiments. To investigate the influence of the indented position, two quasi-static experiments with different numbers of stiffeners were conducted. To predict the initial failure of the stiffened-plate maximum-resistance force up to this point, a semi-analytical approach was established. The results of the proposed semi-analytical approach were compared with the experimental results.
Stiffened plate is a fundamental element of ship and other engineering structures. The crashworthiness and failure mechanism of stiffened plates subjected to lateral indentation by a sphere have been studied extensively by researchers with experimental and theoretical methods.
To investigate the indentation resistance of hull panel during ship grounding, Alsos and Amdahl (2009) conducted a series of scale stiffened plate experiments with quasi-static loading. Meanwhile, Karlsson et al. (2009) conducted two scale quasistatic experiments of ship double-side structure subjected to lateral indentation by a sphere. To investigate the crashworthiness of stiffened plate, Cho and Lee (2009) conducted a series of pendulum impact experiments. Also, extensive analytical or semi-analytical research was conducted to predict the maximum resistance. For theoretical analysis of the clamped plate subjected to lateral indentation by a sphere, much research has been done. For example, Shen et al. (2002) and Shen (2002) presented a theoretical method to predict the onset of failure for thin circular plates struck by a conical indenter. Jones and Birch (2008), Jones et al. (2008), and Jones and Paik (2013) discussed the perforation energy for plates struck by a cylindrical indenter with different impact faces. However, for an analytical or semi-analytical study of clamped stiffener, there is not as much research as on clamped plate. Ohtsubo et al. (1995) proposed a simplified analysis method to discuss the crashworthiness of ship double-side structure subjected to collision by a bulbous bow. In their analysis, the shape of the bulbous bow is simplified as a truncated pyramid. Suzuki et al. (1999) proposed a simplified analysis method to discuss the crashworthiness of ship double-side structure subjected to collision by a wedge bow.
Wendt, Fabian F. (National Wind Technology Center, National Renewable Energy Laboratory) | Robertson, Amy N. (National Wind Technology Center, National Renewable Energy Laboratory) | Jonkman, Jason M. (National Wind Technology Center, National Renewable Energy Laboratory)
During the Offshore Code Comparison Collaboration, Continued, with Correlation (OC5) project, which focused on the validation of numerical methods through comparison against tank test data, the authors created a numerical FAST model of the 1:50-scale DeepCwind semisubmersible system that was tested at the Maritime Research Institute Netherlands ocean basin in 2013. The OC5 project revealed a general underprediction of loads and motions by the participating numerical models. This paper discusses several model calibration studies that were conducted to identify potential model parameter adjustments that help to improve the agreement between the numerical simulations and the experimental test data. These calibration studies cover wind-field-specific parameters (coherence, turbulence), and hydrodynamic and aerodynamic modeling approaches, as well as rotor model (blade-pitch and blade-mass imbalances) and tower model (structural tower damping coefficient) adjustments. These calibration studies were conducted based on relatively simple calibration load cases (wave only/wind only). The agreement between the final FAST model and experimental measurements is then assessed based on more complex combined wind and wave validation cases. The analysis presented in this paper does not claim to be an exhaustive parameter identification study but is aimed at describing the qualitative impact of different model parameters on the system response. This work should help to provide guidance for future systematic parameter identification and uncertainty quantification efforts.
Selker, Ruud (INTECSEA) | Liu, Ping (INTECSEA) | Jurdik, Erich (South Stream Transport BV) | Chaudhuri, Jay (South Stream Transport BV) | Fonzo, Andrea (RINA Consulting-Centro Sviluppo Materiali) | di Biagio, Massimo (RINA Consulting-Centro Sviluppo Materiali)
S-Lay installation of inline buckle arrestors in deep water can introduce plastic strain to girth welds. The welds are repeatedly loaded by large-strain cycles when traversing the stinger. A material-testing program was launched to assess the impact of this load sequence on the welds’ integrity. It is essential to establish the correct mechanism of crack growth caused by a limited number of sequential large-strain cycles. Segment specimens with increased specimen “daylight” length were tested. Fracture morphologies of ductile tearing and fatigue growth were distinguished; ductile tearing was identified only for the first load cycle, whereas subsequent cycles were dominated by fatigue crack growth.
The TurkStream Offshore Pipeline was developed by South Stream Transport BV (SSTTBV). It is a major gas-transmission system that currently comprises two pipeline strings installed in up to 2,200 m water depth, connecting large gas reservoirs in Russia to the Turkish gas-transportation network through the Black Sea. The system currently has a capacity to transport 31.5 bcm of natural gas annually over a distance of more than 900 km. The pipeline’s outer diameter (D) is 32 inches, and its wall thickness (t) is 39 mm. Material grade is DNV SAWL (submerged arc-welded longitudinal) 450 with supplementary requirement F, D, U, and (light) S according to offshore standard DNV-OSF101 (Det Norske Veritas, 2010) plus project-specific modifications. Pipe joints are produced by UOE (U-ing, O-ing and expansion) and JCOE (J-ing, C-ing, O-ing and expansion) pipe-forming methods. Ultra-deep water in combination with the large pipeline diameter makes this project one of the most challenging pipeline projects ever, pushing the boundaries of the industry. The first portion of the pipeline was installed in 2017–2018.
Shibayama, Atsushi (Central Research Institute of Electric Power Industry) | Miyagawa, Yoshinori (Central Research Institute of Electric Power Industry) | Kihara, Naoto (Central Research Institute of Electric Power Industry) | Kaida, Hideki (Central Research Institute of Electric Power Industry)
The damages of the gigantic tsunami that followed the 2011 Great East Japan Earthquake were confirmed on reinforced concrete (RC) structures (Nandasena et al., 2012). Moreover, the damages caused by the tsunami debris collision were confirmed in addition to the damages caused by only the tsunami. Therefore, it is important to clarify the response characteristics of the structure subjected to the tsunami wave force and collision force, and to establish a response evaluation method by numerical analysis. However, the response characteristics of RC structures subjected to two external forces with significantly different timings of actions--namely, wave pressure and collision forces--have not been clarified. Furthermore, to assess the responses of RC structures using numerical analysis, the two different types of superimposing external forces must be considered. However, the applicability of numerical analysis under such external force conditions has not been sufficiently verified. In this research, a large-scale debris collision experiment was first conducted to experimentally investigate the response of an RC vertical wall subjected to the wave pressure and debris collision forces. Next, a reproducibility analysis of the experiment was performed with nonlinear finite element analysis to examine the adaptability of the finite element analysis.
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.
Considering usual computation efforts, single-frame models are used in the ultimate strength analyses of container ships. However, the case of large container ships is more complicated, and further investigations should be made. Generally speaking, the modeling extent, boundary conditions, lateral pressure, and initial deflection are key factors in the ultimate strength analysis. As a case study, we investigated their influences on ultimate strength under both vertical bending and torsion cases for a typical 10,000 twenty-foot equivalent unit (TEU) container ship, and also bending–torsion interactions. The results are representative and can be reference values for container ships of similar sizes.
Container ships are getting larger, and their structural strengths are major concerns for their owners and designers, especially after the 2013 crash of the MOL Comfort, an 8,110 twenty-foot equivalent unit (TEU) container ship. According to technical investigations (ClassNK, 2014), the local deformations of local structures such as double bottom are not negligible, which, however, has not been systematically considered previously. Thus, further investigations of large container ships to better understand their specific structural behaviors are meaningful.