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3: Estimated methane hydrate occurrences in the world. This map is taken from the World Ocean Review [13], and shows the data of Wallmann et al. [75].

3: Estimated methane hydrate occurrences in the world. This map is taken from the World Ocean Review [13], and shows the data of Wallmann et al. [75].

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Thesis
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Elastic and failure properties of methane hydrates are studied using molecular dynamics simulations. The TIP4P/Ice water model and the OPLS united atom methane model are employed in the study. Mechanical properties are reported, and a possible fracture initiation process is identified. On the nanosecond timescale, a pure sI methane hydrate is ident...

Citations

... The fracture toughness of monocrystalline sI hydrate using mW has been estimated to be 0.08 MPa m , 24 which is close to the experimentally reported strengths of pure water ice 32,33 and only slightly higher than the fracture toughness of sI hydrate modeled with TIP4P/ ice. 34 The monatomic water model allows for the growth of both amorphous and crystalline hydrates and can spontaneously produce hydrates where amorphous, sI and sII hydrates coexist. 35 Furthermore, it has been shown that the mW model presents similar mechanical response of polycrystalline hydrates as TIP4P/ice and TIP4P/2005. ...
Article
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The shear failure mechanism of polycrystalline gas hydrates is critical for understanding marine geohazards related to gas hydrates under a changing climate and for safe gas recovery from gas hydrate reservoirs. Since current experimental techniques cannot resolve the mechanism on a spatial and temporal nanoscale, molecular simulations can assist with proposing and substantiating nanoscale failure mechanisms. Here, we report the shear failure of polycrystalline methane hydrates using direct molecular dynamics simulations. Based on these simulations, we suggest two modes of shear behavior, depending on the grain sizes, d, in the polycrystal: grain-size-strengthening behavior with a d1/3 grain size dependence for small grain sizes and grain-size-weakening behavior for large grain sizes. Through the crossover from strengthening to weakening behavior, the failure mode changes from shear failure with a failure plane parallel to the applied shear to tensile failure with a failure plane lying at an angle with the applied shear, spanning a network of grain boundaries. The existence of such a change in mechanism suggests that the Hall–Petch breakdown in methane hydrates is due to a change from grain boundary sliding to tensile opening being the most important failure mechanism when the grain size increases.
... 214 The rapid progress of modern computer technology together with the unavoidable uncertainties associated with the experimental studies means models are the most promising alternative for providing insights into the mechanical behaviour of pure clathrate hydrates. 214 Theoretical approaches such as Density-Functional Theory (DFT), [345][346][347][348][349][350][351][352] Molecular Dynamics (MD) 336,[353][354][355][356][357][358][359][360][361][362][363] and Lattice Dynamics (LD) simulations [364][365][366][367] have been used to probe the mechanical behaviour of clathrate hydrates, with links to macroscopic phenomena. They have also been employed to deliver insights into problems not well understood by experiments and to validate the experimental results. ...
... 349 MD simulations have assisted with the construction of theoretical stress-strain curves for pure clathrate hydrates for different structures and at different pressures and temperatures and led to the determination of such mechanical properties as Poisson's ratio, elastic moduli and strength and identification of fracture initiation process. 353,354,357,359,361 The origin of strain hardening in methane hydrates under compressive deformation was also investigated using MD simulations. The simulation results highlight the role of the guest molecules as nondeformable units preventing the failure of hydrate structures and thus leading to the strain-hardening phenomenon. ...
Article
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Gas hydrates have received considerable attention due to their important role in flow assurance for the oil and gas industry, their extensive natural occurrence on Earth and extraterrestrial planets, and their significant applications in sustainable technologies including but not limited to gas and energy storage, gas separation, and water desalination. Given not only their inherent structural flexibility depending on the type of guest gas molecules and formation conditions, but also the synthetic effects of a wide range of chemical additives on their properties, these variabilities could be exploited to optimise the role of gas hydrates. This includes increasing their industrial applications, understanding and utilising their role in Nature, identifying potential methods for safely extracting natural gases stored in naturally occurring hydrates within the Earth, and for developing green technologies. This review summarizes the different properties of gas hydrates as well as their formation and dissociation kinetics and then reviews the fast-growing literature reporting their role and applications in the aforementioned fields, mainly concentrating on advances during the last decade. Challenges, limitations, and future perspectives of each field are briefly discussed. The overall objective of this review is to provide readers with an extensive overview of gas hydrates that we hope will stimulate further work on this riveting field.