A three-dimensional DEM modelling of triaxial test on gas hydrate-bearing sediments considering flexible boundary condition

The boundary condition design of a three-dimensional furnace that heats an object moving along a conveyor belt of an assembly line is considered. A furnace of this type can be used by the manufacturing industry for applications such as industrial baking, curing of paint, annealing or manufacturing through chemical deposition. The object that is to be heated moves along the furnace as it is heated following a specified temperature history. The spatial temperature distribution on the object is kept isothermal through the whole process. The temperature distribution of the heaters of the furnace should be changed as the object moves so that the specified temperature history can be satisfied. The design problem is transient where a series of inverse problems are solved. The process furnace considered is in the shape of a rectangular tunnel where the heaters are located on the top and the design object moves along the bottom. The inverse design approach is used for the solution, which is advantageous over a traditional trial-and-error solution where an iterative solution is required for every position as the object moves. The inverse formulation of the design problem is ill-posed and involves a set of Fredholm equations of the first kind. The use of advanced solvers that are able to regularize the resulting system is essential. These include the conjugate gradient method, the truncated singular value decomposition or Tikhonov regularization, rather than an ordinary solver, like Gauss-Seidel or Gauss elimination.

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Wave Propagation Characteristics in Gas Hydrate-Bearing Sediments and Estimation of Hydrate Saturation

Energies ◽

10.3390/en14040804 ◽

2021 ◽

Vol 14 (4) ◽

pp. 804

Author(s):

Lin Liu ◽

Xiumei Zhang ◽

Xiuming Wang

Keyword(s):

Gas Hydrate ◽

Clay Content ◽

Clean Energy ◽

Compressional Wave ◽

Physical Parameters ◽

Well Log ◽

Log Data ◽

Phase Velocities ◽

Hydrate Saturation ◽

Hydrate Bearing Sediments

Natural gas hydrate is a new clean energy source in the 21st century, which has become a research point of the exploration and development technology. Acoustic well logs are one of the most important assets in gas hydrate studies. In this paper, an improved Carcione–Leclaire model is proposed by introducing the expressions of frame bulk modulus, shear modulus and friction coefficient between solid phases. On this basis, the sensitivities of the velocities and attenuations of the first kind of compressional (P1) and shear (S1) waves to relevant physical parameters are explored. In particular, we perform numerical modeling to investigate the effects of frequency, gas hydrate saturation and clay on the phase velocities and attenuations of the above five waves. The analyses demonstrate that, the velocities and attenuations of P1 and S1 are more sensitive to gas hydrate saturation than other parameters. The larger the gas hydrate saturation, the more reliable P1 velocity. Besides, the attenuations of P1 and S1 are more sensitive than velocity to gas hydrate saturation. Further, P1 and S1 are almost nondispersive while their phase velocities increase with the increase of gas hydrate saturation. The second compressional (P2) and shear (S2) waves and the third kind of compressional wave (P3) are dispersive in the seismic band, and the attenuations of them are significant. Moreover, in the case of clay in the solid grain frame, gas hydrate-bearing sediments exhibit lower P1 and S1 velocities. Clay decreases the attenuation of P1, and the attenuations of S1, P2, S2 and P3 exhibit little effect on clay content. We compared the velocity of P1 predicted by the model with the well log data from the Ocean Drilling Program (ODP) Leg 164 Site 995B to verify the applicability of the model. The results of the model agree well with the well log data. Finally, we estimate the hydrate layer at ODP Leg 204 Site 1247B is about 100–130 m below the seafloor, the saturation is between 0–27%, and the average saturation is 7.2%.

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Geomechanical properties of gas hydrate-bearing sediments in Shenhu Area of the South China Sea

Energy Reports ◽

10.1016/j.egyr.2021.05.063 ◽

2021 ◽

Author(s):

Jiangong Wei ◽

Lin Yang ◽

Qianyong Liang ◽

Jinqiang Liang ◽

Jingan Lu ◽

...

Keyword(s):

South China Sea ◽

South China ◽

Gas Hydrate ◽

The South China Sea ◽

The South ◽

Shenhu Area ◽

Geomechanical Properties ◽

China Sea ◽

Hydrate Bearing Sediments

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Bootstrapping boundary-localized interactions

Journal of High Energy Physics ◽

10.1007/jhep12(2020)182 ◽

2020 ◽

Vol 2020 (12) ◽

Author(s):

Connor Behan ◽

Lorenzo Di Pietro ◽

Edoardo Lauria ◽

Balt C. van Rees

Keyword(s):

Boundary Condition ◽

Scalar Field ◽

Boundary Conditions ◽

Parameter Space ◽

Three Dimensional ◽

Conformal Boundary ◽

Dimensional Boundary ◽

Dirichlet And Neumann Conditions ◽

Boundary Fields ◽

Boundary Dynamics

Abstract We study conformal boundary conditions for the theory of a single real scalar to investigate whether the known Dirichlet and Neumann conditions are the only possibilities. For this free bulk theory there are strong restrictions on the possible boundary dynamics. In particular, we find that the bulk-to-boundary operator expansion of the bulk field involves at most a ‘shadow pair’ of boundary fields, irrespective of the conformal boundary condition. We numerically analyze the four-point crossing equations for this shadow pair in the case of a three-dimensional boundary (so a four-dimensional scalar field) and find that large ranges of parameter space are excluded. However a ‘kink’ in the numerical bounds obeys all our consistency checks and might be an indication of a new conformal boundary condition.

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An analytical solution of the tide-induced groundwater table overheight under a three-dimensional kinematic boundary condition

Journal of Hydrology ◽

10.1016/j.jhydrol.2021.125986 ◽

2021 ◽

Vol 595 ◽

pp. 125986

Author(s):

Mingzhe Yang ◽

Haijiang Liu ◽

Wenjian Meng

Keyword(s):

Boundary Condition ◽

Analytical Solution ◽

Three Dimensional ◽

Groundwater Table ◽

Kinematic Boundary Condition

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Characterization of elastic properties of near-surface and subsurface deepwater hydrate-bearing sediments

Geophysics ◽

10.1190/geo2012-0385.1 ◽

2013 ◽

Vol 78 (3) ◽

pp. D169-D179 ◽

Cited By ~ 5

Author(s):

Zijian Zhang ◽

De-hua Han ◽

Daniel R. McConnell

Keyword(s):

Wave Velocity ◽

Elastic Constants ◽

Gas Hydrate ◽

Effective Medium Theory ◽

Pore Space ◽

Seismic Interpretation ◽

P Wave ◽

Near Surface ◽

Free Gas ◽

Hydrate Bearing Sediments

Hydrate-bearing sands and shallow nodular hydrate are potential energy resources and geohazards, and they both need to be better understood and identified. Therefore, it is useful to develop methodologies for modeling and simulating elastic constants of these hydrate-bearing sediments. A gas-hydrate rock-physics model based on the effective medium theory was successfully applied to dry rock, water-saturated rock, and hydrate-bearing rock. The model was used to investigate the seismic interpretation capability of hydrate-bearing sediments in the Gulf of Mexico by computing elastic constants, also known as seismic attributes, in terms of seismic interpretation, including the normal incident reflectivity (NI), Poisson’s ratio (PR), P-wave velocity ([Formula: see text]), S-wave velocity ([Formula: see text]), and density. The study of the model was concerned with the formation of gas hydrate, and, therefore, hydrate-bearing sediments were divided into hydrate-bearing sands, hydrate-bearing sands with free gas in the pore space, and shallow nodular hydrate. Although relations of hydrate saturation versus [Formula: see text] and [Formula: see text] are different between structures I and II gas hydrates, highly concentrated hydrate-bearing sands may be interpreted on poststack seismic amplitude sections because of the high NI present. The computations of elastic constant implied that hydrate-bearing sands with free gas could be detected with the crossplot of NI and PR from prestack amplitude analysis, and density may be a good hydrate indicator for shallow nodular hydrate, if it can be accurately estimated by seismic methods.

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