Journal articles on the topic 'Regional-scale 3-D Numerical Modelling'
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1
Ziegler, Moritz O., Oliver Heidbach, John Reinecker, Anna M. Przybycin, and Magdalena Scheck-Wenderoth. "A multi-stage 3-D stress field modelling approach exemplified in the Bavarian Molasse Basin." Solid Earth 7, no. 5 (September 21, 2016): 1365–82. http://dx.doi.org/10.5194/se-7-1365-2016.
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Abstract. The knowledge of the contemporary in situ stress state is a key issue for safe and sustainable subsurface engineering. However, information on the orientation and magnitudes of the stress state is limited and often not available for the areas of interest. Therefore 3-D geomechanical–numerical modelling is used to estimate the in situ stress state and the distance of faults from failure for application in subsurface engineering. The main challenge in this approach is to bridge the gap in scale between the widely scattered data used for calibration of the model and the high resolution in the target area required for the application. We present a multi-stage 3-D geomechanical–numerical approach which provides a state-of-the-art model of the stress field for a reservoir-scale area from widely scattered data records. Therefore, we first use a large-scale regional model which is calibrated by available stress data and provides the full 3-D stress tensor at discrete points in the entire model volume. The modelled stress state is used subsequently for the calibration of a smaller-scale model located within the large-scale model in an area without any observed stress data records. We exemplify this approach with two-stages for the area around Munich in the German Molasse Basin. As an example of application, we estimate the scalar values for slip tendency and fracture potential from the model results as measures for the criticality of fault reactivation in the reservoir-scale model. The modelling results show that variations due to uncertainties in the input data are mainly introduced by the uncertain material properties and missing SHmax magnitude estimates needed for a more reliable model calibration. This leads to the conclusion that at this stage the model's reliability depends only on the amount and quality of available stress information rather than on the modelling technique itself or on local details of the model geometry. Any improvements in modelling and increases in model reliability can only be achieved using more high-quality data for calibration.
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Li, Guodong, Guoding Chen, Pengfeng Li, and Haixiao Jing. "Efficient and Accurate 3-D Numerical Modelling of Landslide Tsunami." Water 11, no. 10 (September 29, 2019): 2033. http://dx.doi.org/10.3390/w11102033.
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High-speed and accurate simulations of landslide-generated tsunamis are of great importance for the understanding of generation and propagation of water waves and for prediction of these natural disasters. A three-dimensional numerical model, based on Reynolds-averaged Navier–Stokes equations, is developed to simulate the landslide-generated tsunami. Available experiment data is used to validate the numerical model and to investigate the scale effect of numerical model according to the Froude similarity criterion. Based on grid convergence index (GCI) analysis, fourteen cases are arranged to study the sensitivity of numerical results to mesh resolution. Results show that numerical results are more sensitive to mesh resolution in near field than that in the propagation field. Nonuniform meshes can be used to balance the computational efficiency and accuracy. A mesh generation strategy is proposed and validated, achieving an accurate prediction and nearly 22 times reduction of computational cost. Further, this strategy of mesh generation is applied to simulate the Laxiwa Reservoir landslide tsunami. The results of this study provide an important guide for the establishment of a numerical model of the real-world problem of landslide tsunami.
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Anabor, V., U. Rizza, G. A. Degrazia, and E. de Lima Nascimento. "Numerical modelling of microburst with Large-Eddy Simulation." Atmospheric Chemistry and Physics Discussions 10, no. 10 (October 20, 2010): 24345–70. http://dx.doi.org/10.5194/acpd-10-24345-2010.
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Abstract. An isolated and stationary microburst is simulated using a 3-D time-dependent, high resolution Large-Eddy Simulation (LES) model. The microburst downdraft is initiated by specifying a simplified cooling source at the top of the domain near 2 km. The modelled time scale for this damaging wind (30 m/s) is of order of few min with a spatial scale enclosing a region with 500 m radius around the impact point. These features are comparable with results obtained from full-cloud models. The simulated flow shows the principal features observed by Doppler radar and others observational full-scale downburst events. In particular are observed the expansion of the primary and secondary cores, the presence of the ring vortex at the leading edge of the cool outflow, and finally an accelerating outburst of surface winds. This result evidences the capability of LES to reproduce complexes phenomena like a Microburst and indicates the potential of LES for utilization in atmospheric phenomena situated below the storm scale and above the microscale, which generally involves high velocities in a short time scale.
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Louis-Napoléon, Aurélie, Muriel Gerbault, Thomas Bonometti, Cédric Thieulot, Roland Martin, and Olivier Vanderhaeghe. "3-D numerical modelling of crustal polydiapirs with volume-of-fluid methods." Geophysical Journal International 222, no. 1 (March 20, 2020): 474–506. http://dx.doi.org/10.1093/gji/ggaa141.
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SUMMARY Gravitational instabilities exert a crucial role on the Earth dynamics and in particular on its differentiation. The Earth’s crust can be considered as a multilayered fluid with different densities and viscosities, which may become unstable in particular with variations in temperature. With the specific aim to quantify crustal scale polydiapiric instabilities, we test here two codes, JADIM and OpenFOAM, which use a volume-of-fluid (VOF) method without interface reconstruction, and compare them with the geodynamics community code ASPECT, which uses a tracking algorithm based on compositional fields. The VOF method is well-known to preserve strongly deforming interfaces. Both JADIM and OpenFOAM are first tested against documented two and three-layer Rayleigh–Taylor instability configurations in 2-D and 3-D. 2-D and 3-D results show diapiric growth rates that fit the analytical theory and are found to be slightly more accurate than those obtained with ASPECT. We subsequently compare the results from VOF simulations with previously published Rayleigh–Bénard analogue and numerical experiments. We show that the VOF method is a robust method adapted to the study of diapirism and convection in the Earth’s crust, although it is not computationally as fast as ASPECT. OpenFOAM is found to run faster than, and conserve mass as well as JADIM. Finally, we provide a preliminary application to the polydiapiric dynamics of the orogenic crust of Naxos Island (Greece) at about 16 Myr, and propose a two-stages scenario of convection and diapirism. The timing and dimensions of the modelled gravitational instabilities not only corroborate previous estimates of timing and dimensions associated to the dynamics of this hot crustal domain, but also bring preliminary insight on its rheological and tectonic contexts.
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Leng, K., J. Korenaga, and T. Nissen-Meyer. "3-D scattering of elastic waves by small-scale heterogeneities in the Earth’s mantle." Geophysical Journal International 223, no. 1 (July 8, 2020): 502–25. http://dx.doi.org/10.1093/gji/ggaa331.
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SUMMARY Small-scale heterogeneities in the Earth’s mantle, the origin of which is likely compositional anomalies, can provide critical clues on the evolution of mantle convection. Seismological investigation of such small-scale heterogeneities can be facilitated by forward modelling of elastic wave scattering at high frequencies, but doing so with conventional 3-D numerical methods has been computationally prohibitive. We develop an efficient approach for computing high-frequency synthetic wavefields originating from small-scale mantle heterogeneities. Our approach delivers the exact elastodynamic wavefield and does not restrict the geometry or physical properties of the local heterogeneity and the background medium. It combines the technique of wavefield injection and a numerical method called AxiSEM3D. Wavefield injection can decompose the total wavefield into an incident and a scattered part. Both these two parts naturally have low azimuthal complexity and can thus be solved efficiently using AxiSEM3D under two different coordinate systems. With modern high-performance computing (on an order of magnitude of 105 CPU-hr), we have achieved a 1 Hz dominant frequency for global-scale problems with strong deep Earth scattering. Compared with previous global injection approaches, ours allows for a 3-D background medium and yields the exact solution without ignoring any higher-order scattering by the background medium. Technically, we develop a traction-free scheme for realizing wavefield injection in a spectral element method, which brings in several flexibilities and simplifies the implementation by avoiding stress or traction computation on the injection boundary. For a spherical heterogeneity in the mid-lower mantle, we compare the 3-D full-wave solution with two approximate ones obtained, respectively, by the perturbation theory and in-plane (axisymmetric) modelling. As a comprehensive application, we study S-wave scattering by a 3-D ultra-low velocity zone, incorporating 3-D crustal structures on the receiver side as part of the background model.
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Lin, X., and Y. Tao. "A numerical modelling study on regional mercury budget for eastern North America." Atmospheric Chemistry and Physics Discussions 3, no. 1 (February 20, 2003): 983–1015. http://dx.doi.org/10.5194/acpd-3-983-2003.
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Abstract. In this study, we have integrated an up-to-date physio-chemical transformation mechanism of Hg into the framework of US EPA's CMAQ model system. In addition, the model adapted detailed calculations of the air-surface exchange for Hg to properly describe Hg re-emissions and dry deposition from and to natural surfaces. The mechanism covers Hg in three categories, elemental Hg (Hg0), reactive gaseous Hg (RGM) and particulate Hg (HgP). With interfacing to MM5 (meteorology processor) and SMOKE (emission processor), we applied the model to a 4-week period in June/July 1995 on a domain covering most of eastern North America. Results indicate that the model simulates reasonably well the levels of total gaseous Hg (TGM) and the specific Hg wet deposition measurements made by the Hg deposition network (MDN). Moreover, results from various scenario runs reveal that the Hg system behaves in a closely linear way in terms of contributions from different source categories, i.e. anthropogenic emissions, natural re-emissions and background. Analyses of the scenario results suggest that 37% of anthropogenically emitted Hg was deposited back in the model domain with 5155.2 kg of anthropogenic Hg moving out of the domain during the simulation period. Overall, the domain served as a source, which supplied a net 461.2 kg of Hg to the global background pool over the period. Our model validation and a sensitivity test further rationalized the rate constant for gaseous oxidation of Hg0 by hydroxyl radical OH used in the global scale modelling study by Bergan and Rodhe (2001). A further laboratory determination of the reaction rate constant, including its temperature dependence, stands as one of the important issues critical to improving our knowledge on the budget and cycling of Hg.
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Lin, X., and Y. Tao. "A numerical modelling study on regional mercury budget for eastern North America." Atmospheric Chemistry and Physics 3, no. 3 (May 26, 2003): 535–48. http://dx.doi.org/10.5194/acp-3-535-2003.
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Abstract. In this study, we have integrated an up-to-date physio-chemical transformation mechanism of Hg into the framework of US EPA's CMAQ model system. In addition, the model adapted detailed calculations of the air-surface exchange for Hg to properly describe Hg re-emissions and dry deposition from and to natural surfaces. The mechanism covers Hg in three categories, elemental Hg (Hg0), reactive gaseous Hg (RGM) and particulate Hg (HgP). With interfacing to MM5 (meteorology processor) and SMOKE (emission processor), we applied the model to a 4-week period in June/July 1995 on a domain covering most of eastern North America. Results indicate that the model simulates reasonably well the levels of total gaseous Hg (TGM) and the specific Hg wet deposition measurements made by the Hg deposition network (MDN). Moreover, results from various scenario runs reveal that the Hg system behaves in a closely linear way in terms of contributions from different source categories, i.e. anthropogenic emissions, natural re-emissions and background. Analyses of the scenario results suggest that 37% of anthropogenically emitted Hg was deposited back in the model domain with 5155 kg of anthropogenic Hg moving out of the domain during the simulation period. Overall, the domain served as a net source, which supplied ~a half ton of Hg to the global background pool over the period. Our model validation and a sensitivity test further rationalized the rate constant for gaseous oxidation of Hg0 by hydroxyl radical OH used in the global scale modelling study by Bergan and Rodhe (2001). A further laboratory determination of the reaction rate constant, including its temperature dependence, stands as one of the important issues critical to improving our knowledge on the budget and cycling of Hg.
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Mensah, Victor, and Arturo Hidalgo. "Modelling the effects of diffusive-viscous waves in a 3-D fluid-saturated media using two numerical approaches." Geophysical Journal International 224, no. 2 (September 24, 2020): 1443–63. http://dx.doi.org/10.1093/gji/ggaa457.
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SUMMARY The accurate numerical modelling of 3-D seismic wave propagation is essential in understanding details to seismic wavefields which are, observed on regional and global scales on the Earth’s surface. The diffusive-viscous wave (DVW) equation was proposed to study the connection between fluid saturation and frequency dependence of reflections and to characterize the attenuation property of the seismic wave in a fluid-saturated medium. The attenuation of DVW is primarily described by the active attenuation parameters (AAP) in the equation. It is, therefore, imperative to acquire these parameters and to additionally specify the characteristics of the DVW. In this paper, quality factor, Q is used to obtain the AAP, and they are compared to those of the visco-acoustic wave. We further derive the 3-D numerical schemes based on a second order accurate finite-volume scheme with a second order Runge–Kutta approximation for the time discretization and a fourth order accurate finite-difference scheme with a fourth order Runge–Kutta approximation for the time discretization. We then simulate the propagation of seismic waves in a 3-D fluid-saturated medium based on the derived schemes. The numerical results indicate stronger attenuation when compared to the visco-acoustic case.
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Fischer, K., and A. Henk. "3-D geomechanical modelling of a gas reservoir in the North German Basin: workflow for model building and calibration." Solid Earth Discussions 5, no. 1 (June 7, 2013): 767–88. http://dx.doi.org/10.5194/sed-5-767-2013.
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Abstract. The optimal use of conventional and unconventional hydrocarbon reservoirs depends, amongst others, on the local tectonic stress field. For example, wellbore stability, orientation of hydraulically induced fractures and – especially in fractured reservoirs – permeability anisotropies are controlled by the recent in situ stresses. Faults and lithological changes can lead to stress perturbations and produce local stresses that can significantly deviate from the regional stress field. Geomechanical reservoir models aim for a robust, ideally "pre-drilling" prediction of the local variations in stress magnitude and orientation. This requires a~numerical modelling approach that is capable to incorporate the specific geometry and mechanical properties of the subsurface reservoir. The workflow presented in this paper can be used to build 3-D geomechanical models based on the Finite Element Method (FEM) and ranging from field-scale models to smaller, detailed submodels of individual fault blocks. The approach is successfully applied to an intensively faulted gas reservoir in the North German Basin. The in situ stresses predicted by the geomechanical FE model were calibrated against stress data actually observed, e.g. borehole breakouts and extended leak-off tests. Such a validated model can provide insights into the stress perturbations in the inter-well space and undrilled parts of the reservoir. In addition, the tendency of the existing fault network to slip or dilate in the present-day stress regime can be addressed.
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Arasa, R., M. R. Soler, and M. Olid. "Evaluating the Performance of a Regional-Scale Photochemical Modelling System: Part I—Ozone Predictions." ISRN Meteorology 2012 (November 29, 2012): 1–22. http://dx.doi.org/10.5402/2012/860234.
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We present a detailed evaluation of the seasonal performance of the Community Multiscale Air Quality (CMAQ) modelling system and the PSU/NCAR meteorological model coupled to a new Numerical Emission Model for Air Quality (MNEQA). The combined system simulates air quality at a fine resolution (3 km as horizontal resolution and 1 h as temporal resolution) in north-eastern Spain, where problems of ozone pollution are frequent. An extensive database compiled over two periods, from May to September 2009 and 2010, is used to evaluate meteorological simulations and chemical outputs. Our results indicate that the model accurately reproduces hourly and 1-h and 8-h maximum ozone surface concentrations measured at the air quality stations, as statistical values fall within the EPA and EU recommendations. However, to further improve forecast accuracy, three simple bias-adjustment techniques—mean subtraction (MS), ratio adjustment (RA), and hybrid forecast (HF)—based on 10 days of available comparisons are applied. The results show that the MS technique performed better than RA or HF, although all the bias-adjustment techniques significantly reduce the systematic errors in ozone forecasts.
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Drago, A. F., R. Sorgente, and A. Ribotti. "A high resolution hydrodynamic 3-D model simulation of the malta shelf area." Annales Geophysicae 21, no. 1 (January 31, 2003): 323–44. http://dx.doi.org/10.5194/angeo-21-323-2003.
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Abstract. The seasonal variability of the water masses and transport in the Malta Channel and proximity of the Maltese Islands have been simulated by a high resolution (1.6 km horizontal grid on average, 15 vertical sigma layers) eddy resolving primitive equation shelf model (ROSARIO-I). The numerical simulation was run with climatological forcing and includes thermohaline dynamics with a turbulence scheme for the vertical mixing coefficients on the basis of the Princeton Ocean Model (POM). The model has been coupled by one-way nesting along three lateral boundaries (east, south and west) to an intermediate coarser resolution model (5 km) implemented over the Sicilian Channel area. The fields at the open boundaries and the atmospheric forcing at the air-sea interface were applied on a repeating "perpetual" year climatological cycle. The ability of the model to reproduce a realistic circulation of the Sicilian-Maltese shelf area has been demonstrated. The skill of the nesting procedure was tested by model-modelc omparisons showing that the major features of the coarse model flow field can be reproduced by the fine model with additional eddy space scale components. The numerical results included upwelling, mainly in summer and early autumn, along the southern coasts of Sicily and Malta; a strong eastward shelf surface flow along shore to Sicily, forming part of the Atlantic Ionian Stream, with a presence throughout the year and with significant seasonal modulation, and a westward winter intensified flow of LIW centered at a depth of around 280 m under the shelf break to the south of Malta. The seasonal variability in the thermohaline structure of the domain and the associated large-scale flow structures can be related to the current knowledge on the observed hydrography of the area. The level of mesoscale resolution achieved by the model allowed the spatial and temporal evolution of the changing flow patterns, triggered by internal dynamics, to be followed in detail. This modelling effort has initiated the treatment of the open boundary conditions problem in view of the future implementation of shelf-scale real-time ocean forecasting through the sequential nesting of a hierarchy of successively embedded model domains for the downscaling of the hydrodynamics from the coarse grid Ocean General Circulation Model of the whole Mediterranean Sea to finer grids in coastal areas. Key words. Oceanography: general (continental shelf processes; numerical modelling) Oceanography: physical (general circulation)
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Yang, Guoxiang, Anthony K. Leung, Nengxiong Xu, Kunxiang Zhang, and Kunpeng Gao. "Three-Dimensional Physical and Numerical Modelling of Fracturing and Deformation Behaviour of Mining-Induced Rock Slopes." Applied Sciences 9, no. 7 (March 31, 2019): 1360. http://dx.doi.org/10.3390/app9071360.
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Fracturing behaviour of jointed rock mass subjected to mining can significantly affect the stability of the rock structures and rock slopes. Ore mining within an open-pit final slope would lead to large-scale strata and surface movement of the rock slope. Rock mass structure, or more specifically, the strength, spacing and distribution of rock joints, are the controlling factors that govern the failure and deformation mechanisms of the final slope. Two-dimensional (2-D) physical modelling tests have been conducted in the literature, but in general, most of them have simplified the geological conditions and neglected some key features of rock mass structure in the field. In this study, new three-dimensional (3-D) physical modelling methods are introduced, with realistic modelling of mechanical behaviour of rock mass as well as identified properties of predominant rock joint sets. A case study of Yanqianshan iron mine is considered and the corresponding 1:200 model rock slope was created for studying the rock joint effects on the strata movement and the subsidence mechanism of the slope. The physical model test results are subsequently verified with 3-D discrete element numerical modelling. Due to the presence of the predominant joints, the observed well-shaped strata subsidence in Yanqianshan iron mine was successfully reproduced in the 3-D physical model. The failure mechanism of rock slopes differs from the trumpet-shaped subsidence observed in unconsolidated soil. Due to the formation of an arching mechanism within the rock mass, the strata deformation transferred gradually from the roof of the goaf to the slope surface.
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Lin, Lin, Jin-Zhong Yang, Bin Zhang, and Yan Zhu. "A Simplified Numerical Model of 3-D Groundwater and Solute Transport at Large Scale Area." Journal of Hydrodynamics 22, no. 3 (June 2010): 319–28. http://dx.doi.org/10.1016/s1001-6058(09)60061-5.
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Castillo-Reyes, Octavio, Josep de la Puente, Luis Emilio García-Castillo, and José María Cela. "Parallel 3-D marine controlled-source electromagnetic modelling using high-order tetrahedral Nédélec elements." Geophysical Journal International 219, no. 1 (June 24, 2019): 39–65. http://dx.doi.org/10.1093/gji/ggz285.
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SUMMARY We present a parallel and high-order Nédélec finite element solution for the marine controlled-source electromagnetic (CSEM) forward problem in 3-D media with isotropic conductivity. Our parallel Python code is implemented on unstructured tetrahedral meshes, which support multiple-scale structures and bathymetry for general marine 3-D CSEM modelling applications. Based on a primary/secondary field approach, we solve the diffusive form of Maxwell’s equations in the low-frequency domain. We investigate the accuracy and performance advantages of our new high-order algorithm against a low-order implementation proposed in our previous work. The numerical precision of our high-order method has been successfully verified by comparisons against previously published results that are relevant in terms of scale and geological properties. A convergence study confirms that high-order polynomials offer a better trade-off between accuracy and computation time. However, the optimum choice of the polynomial order depends on both the input model and the required accuracy as revealed by our tests. Also, we extend our adaptive-meshing strategy to high-order tetrahedral elements. Using adapted meshes to both physical parameters and high-order schemes, we are able to achieve a significant reduction in computational cost without sacrificing accuracy in the modelling. Furthermore, we demonstrate the excellent performance and quasi-linear scaling of our implementation in a state-of-the-art high-performance computing architecture.
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Reiter, Karsten, Steffen Ahlers, Sophia Morawietz, Luisa Röckel, Tobias Hergert, Andreas Henk, Birgit Müller, and Oliver Heidbach. "The SpannEnD project: 3-D stress prediction in the upper crust of Germany." Safety of Nuclear Waste Disposal 1 (November 10, 2021): 75–76. http://dx.doi.org/10.5194/sand-1-75-2021.
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Abstract. Assessment of the stability of deep geological repositories is a key task in the site selection process for high-level radioactive waste. Geomechanical stability is affected by endogenous and exogenous processes as well as by geotechnical operations. Stability prediction requires both an estimate of future stress changes as well as the initial, i.e. current stress state. However, data records on the current stress state in the upper crust are incomplete, sparse and spatially unevenly distributed. Therefore, geomechanical-numerical models are the only way to estimate the full stress tensor at locations where stress observations are not available. The main components of such a 3-D geomechanical model are the distribution of the elastic rock properties and rock density as well as stress data for the model calibration. The aim is to find the optimal initial and boundary conditions that result in a best-fit with respect to available stress data within the model volume. For this reason, the first open access database for stress magnitude data has been developed as an extension of the existing database on stress orientation data (world-stress-map.org). The new database contains 568 data records from Germany and surrounding areas, but only 15 % of these data records are of acceptable quality. Thus, only one reliable set of stress magnitude data is available for an area of 100×100 km2. Based on existing compilations of the crustal structure in and around Germany, data were merged into one model with the aim of estimating the 3-D stress state in Germany. Geomechanical models for stress estimation in Germany were created with varying geometrical and mechanical resolution. While the first model consists of four mechanical units and 1.3 million finite elements, the subsequent model consists of 12 units and 3.6 million finite elements. The results of the best-fit model with respect to the stress data reveal that there are regional differences when calculating the fracture potential, i.e. the distance to failure of intact rock as well as different values of slip tendency, which provides a measure of the reactivation potential of pre-existing faults. The observed variability of the modelled stress field can be used as a first-order assessment. Since model uncertainties are still high, the absolute values are not yet reliable. However, the model can be used to derive consistent initial and boundary conditions for models on a regional scale. Furthermore, it makes it possible to investigate the influence of the large-scale crustal structure on the overall stress pattern. The modelling workflow is set-up in a way that new information and higher resolution if needed can be implemented when more data are provided. This will improve the reliability of both, the model prediction on the large scale as well as the initial and boundary conditions for high-resolution regional models for selected areas during the site selection process.
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Zhang, H., G. D. Egbert, A. D. Chave, Q. Huang, A. Kelbert, and S. Y. Erofeeva. "Constraints on the resistivity of the oceanic lithosphere and asthenosphere from seafloor ocean tidal electromagnetic measurements." Geophysical Journal International 219, no. 1 (July 11, 2019): 464–78. http://dx.doi.org/10.1093/gji/ggz315.
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SUMMARY The electromagnetic (EM) field generated by ocean tidal flow is readily detectable in both satellite magnetic field data, and in ocean-bottom measurements of electric and magnetic fields. The availability of accurate charts of tidal currents, constrained by assimilation of modern satellite altimetry data, opens the possibility of using tidal EM fields as a source to image mantle electrical resistivity beneath the ocean basins, as highlighted by the recent success in defining the globally averaged lithosphere–asthenosphere boundary (LAB) with satellite data. In fact, seafloor EM data would be expected to provide better constraints on the structure of resistive oceanic lithosphere, since the toroidal magnetic mode, which can constrain resistive features, is a significant component of the tidal EM field within the ocean, but is absent above the surface (in particular in satellite data). Here we consider this issue in more detail, using a combination of simplified theoretical analysis and 1-D and 3-D numerical modelling to provide a thorough discussion of the sensitivity of satellite and seafloor data to subsurface electrical structure. As part of this effort, and as a step toward 3-D inversion of seafloor tidal data, we have developed a new flexible 3-D spherical-coordinate finite difference scheme for both global and regional scale modelling, with higher resolution models nested in larger scale solutions. We use the new 3-D model, together with Monte Carlo simulations of errors in tidal current estimates, to provide a quantitative assessment of errors in the computed tidal EM signal caused by uncertainty in the tidal source. Over the open ocean this component of error is below 0.01 nT in Bz at satellite height and 0.05 nT in Bx on the seafloor, well below typical signal levels. However, as coastlines are approached error levels can increase substantially. Both analytical and 3-D modelling demonstrate that the seafloor magnetic field is most sensitive to the lithospheric resistance (the product of resistivity and thickness), and is more weakly influenced (primarily in the phase) by resistivity of the underlying asthenosphere. Satellite data, which contain only the poloidal magnetic mode, are more sensitive to the conductive asthenosphere, but have little sensitivity to lithospheric resistance. For both seafloor and satellite data’s changes due to plausible variations in Earth parameters are well above error levels associated with source uncertainty, at least in the ocean interior. Although the 3-D modelling results are qualitatively consistent with theoretical analysis, the presence of coastlines and bathymetric variations generates a complex response, confirming that quantitative interpretation of ocean tidal EM fields will require a 3-D treatment. As an illustration of the nested 3-D scheme, seafloor data at five magnetic and seven electric stations in the northeastern Pacific (41○N, 165○W) are fit with trial-and-error forward modelling of a local domain. The simulation results indicate that the lithospheric resistance is roughly 7 × 108 Ωm2. The phase of the seafloor data in this region are inconsistent with a sharp transition between the resistive lithosphere and conductive asthenosphere.
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Burwicz, Ewa, and Matthias Haeckel. "Basin-scale estimates on petroleum components generation in the Western Black Sea basin based on 3-D numerical modelling." Marine and Petroleum Geology 113 (March 2020): 104122. http://dx.doi.org/10.1016/j.marpetgeo.2019.104122.
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Marmy, Antoine, Jan Rajczak, Reynald Delaloye, Christin Hilbich, Martin Hoelzle, Sven Kotlarski, Christophe Lambiel, et al. "Semi-automated calibration method for modelling of mountain permafrost evolution in Switzerland." Cryosphere 10, no. 6 (November 15, 2016): 2693–719. http://dx.doi.org/10.5194/tc-10-2693-2016.
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Abstract. Permafrost is a widespread phenomenon in mountainous regions of the world such as the European Alps. Many important topics such as the future evolution of permafrost related to climate change and the detection of permafrost related to potential natural hazards sites are of major concern to our society. Numerical permafrost models are the only tools which allow for the projection of the future evolution of permafrost. Due to the complexity of the processes involved and the heterogeneity of Alpine terrain, models must be carefully calibrated, and results should be compared with observations at the site (borehole) scale. However, for large-scale applications, a site-specific model calibration for a multitude of grid points would be very time-consuming. To tackle this issue, this study presents a semi-automated calibration method using the Generalized Likelihood Uncertainty Estimation (GLUE) as implemented in a 1-D soil model (CoupModel) and applies it to six permafrost sites in the Swiss Alps. We show that this semi-automated calibration method is able to accurately reproduce the main thermal condition characteristics with some limitations at sites with unique conditions such as 3-D air or water circulation, which have to be calibrated manually. The calibration obtained was used for global and regional climate model (GCM/RCM)-based long-term climate projections under the A1B climate scenario (EU-ENSEMBLES project) specifically downscaled at each borehole site. The projection shows general permafrost degradation with thawing at 10 m, even partially reaching 20 m depth by the end of the century, but with different timing among the sites and with partly considerable uncertainties due to the spread of the applied climatic forcing.
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Frick, Maximilian, Magdalena Scheck-Wenderoth, Mauro Cacace, and Michael Schneider. "Boundary condition control on inter-aquifer flow in the subsurface of Berlin (Germany) – new insights from 3-D numerical modelling." Advances in Geosciences 49 (August 6, 2019): 9–18. http://dx.doi.org/10.5194/adgeo-49-9-2019.
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Abstract. We investigate the degree of hydraulic interconnection between the different (regional to local) groundwater compartments with respect to the choice of boundary conditions and their impact onto the groundwater safety beneath the urban centre of Berlin, capital city of Germany. To this end, we carry out a systematic study based on 3-D hydrothermal models differing in terms of imposed parametric set-ups of the hydrogeology, as well as different surface forcing with respect to their impact on fresh groundwater production. The study area is part of the Northeast German Basin and consists of a thick sequence (up to 5 km) of differently consolidated sedimentary deposits. This sedimentary succession features a sequence of alternating aquifers (reservoirs) and aquitards which are connected to different degrees, each one depicting a specific composition of its mineralised pore water. The uppermost aquifer system (made up mainly of poorly consolidated siliciclastic rocks) acts as the main freshwater reservoir used for groundwater production by the municipal water supplier. This compartment is incompletely sealed from the brackish to saline aquifers extending at greater depths by a regional clay-enriched aquitard, the Oligocene Rupelian Clay. The latter shows a heterogeneous thickness distribution due to erosion during the latest glacial periods resulting in local discontinuities. This aspect opens to the potential risk of contamination of the drinking water reservoir from mixing with the saline groundwater upconing, locally enhanced by shallow pumping activities. Based on our results and their correlation with available isotopic and chemical analysis of water samples, we demonstrate how hydraulic connection between the different compartments is indeed likely to occur thus supporting the possibility of a contaminant rise from the saline aquifers below through either natural or anthropogenic (pumping) forcing.
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Cao, Jian, Romain Brossier, Andrzej Górszczyk, Ludovic Métivier, and Jean Virieux. "3-D multiparameter full-waveform inversion for ocean-bottom seismic data using an efficient fluid–solid coupled spectral-element solver." Geophysical Journal International 229, no. 1 (November 27, 2021): 671–703. http://dx.doi.org/10.1093/gji/ggab484.
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SUMMARY Ocean-bottom seismic acquisition systems deployed on the seabed give access to three-component geophone data and hydrophone data. Compared with conventional streamer acquisitions, the separation of sources and receivers makes it possible to increase the maximum offset and azimuth coverage for improving the illumination at depth. Furthermore, the three-component geophones naturally capture elastic wave propagation effects. While this information is mostly overlooked up to now, reconstructing jointly P- and S-wave velocities would significantly improve the subsurface characterization. To achieve a 3-D high-resolution multiparameter reconstruction, we design an efficient 3-D fluid–solid coupled full waveform modelling and inversion engine. In this engine, fluid and solid domains are divided explicitly and handled with the acoustic and elastic wave equations, respectively. The numerical implementation is based on a time-domain spectral-element method (SEM) with a flexible 3-D Cartesian-based hexahedral mesh, which contributes to an accurate coupling of the acoustic and elastic wave equations and high computational efficiency through domain-decomposition based parallelization. We select the best acoustic–elastic coupled formulations among 4 possibilities with criteria based on numerical accuracy and implementation efficiency. Moreover, we propose a specific hybrid approach for the misfit gradient building so as to use a similar modelling solver for both forward and adjoint simulations. Synthetic case studies on a 3-D extended Marmousi-II model and a 3-D deep-water crustal-scale model illustrate how our modelling and inversion engine can efficiently extract information from ocean-bottom seismic data to simultaneously reconstruct both P- and S-wave velocities within a full waveform inversion framework.
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Crosta, G. B., and F. Agliardi. "A methodology for physically based rockfall hazard assessment." Natural Hazards and Earth System Sciences 3, no. 5 (October 31, 2003): 407–22. http://dx.doi.org/10.5194/nhess-3-407-2003.
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Abstract. Rockfall hazard assessment is not simple to achieve in practice and sound, physically based assessment methodologies are still missing. The mobility of rockfalls implies a more difficult hazard definition with respect to other slope instabilities with minimal runout. Rockfall hazard assessment involves complex definitions for "occurrence probability" and "intensity". This paper is an attempt to evaluate rockfall hazard using the results of 3-D numerical modelling on a topography described by a DEM. Maps portraying the maximum frequency of passages, velocity and height of blocks at each model cell, are easily combined in a GIS in order to produce physically based rockfall hazard maps. Different methods are suggested and discussed for rockfall hazard mapping at a regional and local scale both along linear features or within exposed areas. An objective approach based on three-dimensional matrixes providing both a positional "Rockfall Hazard Index" and a "Rockfall Hazard Vector" is presented. The opportunity of combining different parameters in the 3-D matrixes has been evaluated to better express the relative increase in hazard. Furthermore, the sensitivity of the hazard index with respect to the included variables and their combinations is preliminarily discussed in order to constrain as objective as possible assessment criteria.
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Gonçalvès, Julio, Sophie Violette, Cécile Robin, Maurice Pagel, François Guillocheau, Ghislain de Marsily, Dominique Bruel, and Emmanuel Ledoux. "3-D modelling of salt and heat transport during the 248 m.y. evolution of the Paris basin : diagenetic implications." Bulletin de la Société Géologique de France 174, no. 5 (September 1, 2003): 429–39. http://dx.doi.org/10.2113/174.5.429.
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Abstract A 3-D model of the Paris basin was constructed to reconstitute its 248 m.y. geologic history from the Trias to the present. The model is based on detailed stratigraphic and lithographic data from about 1,100 petroleum drillings. Its scale is regional and it covers a surface area of 700,000 km2, which exceeds the present extent of the basin in order to allow the paleogeographic evolution of the European plate to be taken into account. The geological history is simulated with the numerical model NEWBAS from the Ecole des Mines de Paris. The model simulates sedimentation, erosion, compaction, fluid flow and processes of solute and heat transport. The objective of this article is to demonstrate the value of this type of modelling for estimating and quantifying the role of fluid circulation in geological processes. Studies of diagenetic cements in the Dogger and Keuper aquifers in the Paris basin have often led their authors to consider the involvement of regional fluid circulation. These studies provide estimates of paleotemperature and paleosalinity which impose constraints on the modelling but the latter may, in turn, contribute to date the events and estimate the relevant processes. By reconstructing heat and salt transport, as proposed in this article, it is therefore possible to define the influence of hydrodynamics on these processes. The history of heat and salt in the basin is shown at various stages on a representative NW-SE cross-section of a present-day flow line which is also valid for Tertiary times. We demonstrate that the role of hydrodynamics may be predominant for salt transport by gravity-driven flow, which explains the salinity increase in the Keuper aquifer and the role of the Bray fault in the salinisation of the Dogger. Although the heat transport is dominated by the conductive component, it is also influenced by the hydrodynamics with a possible convective cooling effect when the head in the aquifers increased at the end of the Tertiary erosion period. This may partly explain the higher temperatures, deduced from fluid inclusions in the Keuper, at the end of the chalk deposition as compared to present ones. According to our simulations, the early Tertiary is the period most compatible with the diagenetic observations for thermal (maximum burial and convective cooling effect) and chemical reasons (topography allowing migration of brines in the Keuper and the Dogger).
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Liu, Y. J., and L. Shen. "A dual BIE approach for large-scale modelling of 3-D electrostatic problems with the fast multipole boundary element method." International Journal for Numerical Methods in Engineering 71, no. 7 (2007): 837–55. http://dx.doi.org/10.1002/nme.2000.
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Allen, R., M. J. Siegert, and A. J. Payne. "Reconstructing glacier-based climates of LGM Europe and Russia – Part 1: Numerical modelling and validation methods." Climate of the Past Discussions 3, no. 5 (October 26, 2007): 1133–66. http://dx.doi.org/10.5194/cpd-3-1133-2007.
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Abstract. The mountain environments of mid-latitude Europe and Arctic Russia contain widespread evidence of Late-Quaternary glaciers that have been prescribed to the Last Glacial Maximum (LGM). This glacial-geological record has yet to be used to quantitatively reconstruct the LGM climate of these regions. Here we describe a simple glacier-climate model that can be used to derive regional temperature and precipitation information from a known glacier distribution. The model was tested against the present day distribution of glaciers in Europe. The model is capable of adequately predicting the spatial distribution, snowline and equilibrium line altitude climate of glaciers in the Alps, Scandinavia, Caucasus and Pyrenees Mountains. This verification demonstrated that the model can be used to investigate former climates such as the LGM. Reconstructions of LGM climates from proxy evidence are an important method of assessing retrospective general circulation model (GCM) simulations. LGM palaeoclimate reconstructions from glacial-geological evidence would be of particular benefit to investigations in Europe and Russia, where to date only fossil pollen data have been used to assess continental-scale GCM simulations.
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Vilfayeau, Jerome, David Crépin, François Boussu, Damien Soulat, and Philippe Boisse. "Numerical Modelling of the Weaving Process for Textile Composite." Key Engineering Materials 554-557 (June 2013): 472–77. http://dx.doi.org/10.4028/www.scientific.net/kem.554-557.472.
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Due to advancements made in 3D weaving process [1] and, in order to develop 3D textile structure as reinforcement of composite material for aeronautic application, a good prediction of the geometry and the mechanical properties of the 3D woven unit cell is required. Due to the complexity of these textile architectures, realistic geometric representations [2] of fabrics are often difficult to obtain especially for 3D woven fabrics, but these descriptions are necessary to define meshes for finite element computation [3]. At present, existing tools which model and define, early at a mesoscopic scale [4], the architecture of 3D fabrics don’t take into account the influence of the manufacturing process on the shape modification of the textile structure. Some numerical model exists for the braiding process [5] and the knitting process [6], but not yet for the weaving process. During the manufacturing process, fibres are subjected to significant deformations due to loads from the component of the loom or from the friction with the others fibres. These significant deformations lead to mechanical strength losses of the fabric. A numerical model of the different steps of the weaving process could predict these significant deformations and their influence on the geometry of the textile architecture. Thus, the objective of the NUMTISS project is to develop a numerical model of the deformation of the yarn during the weaving process. For the numerical modelling of the weaving process developed in finite element method, we considered all loom elements like rigid solid, and we will make the assumption that yarns are transverse isotropic elastic materials. Simulations of the process for a plain weave, a twill 2-2 and a satin 8 fabric have already been performed, as well as the simulation of orthogonal warp interlock structures. Then, to understand the kinematic motions of weaving process, the tracking of some strategic elements on the industrial weaving loom (reed, heddles, rapier,..) have been carried out. The tracking obtained from the video of the high speed camera will help us to define the numerical model of the weaving kinematic closer to reality. Correlations between numerical results and specific structures in glass fibres produced on the loom will be presented. The influence of each step of the manufacturing process on the characteristics of the textile structure could be analyzed [1]X. Chen, L. W. Taylor, L. J.Tsai. ”An overview on fabrication of three-dimensional woven textile preforms for composites”. Textile Research Journal, 2011, 81(9) 932–944 [2] SV Lomov, G Perie, DS Ivanov, I Verpoest and D Marsal. “Modeling three-dimensional fabrics and three-dimensional reinforced composites: challenges and solutions”. Textile Research Journal, 2011, 81(1) 28–41 [3] E. De Luycker, F. Morestin, P. Boisse, D. Marsal. « Simulation of 3D interlock composite performing”. Composite Structures, Volume 88, Issue 4, May 2009, Pages 615-623. [4] M. Ansar, W. Xinwei, Z. Chouwei. “Modeling strategies of 3D woven composites: A review”. Composite Structures 93 (2011) 1947–1963. [5] A. K. Pickett, J. Sirtautas, et A. Erber. « Braiding simulation and prediction of mechanical properties”. Applied Composite Materials, 2009. [6] M. Duhovic, D. Bhattacharyya. “Simulating the deformation mechanisms of knitted fabric composites”. Composites Part A : Applied Science and Manufacturing, 2006.
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Fischer, K., and A. Henk. "A workflow for building and calibrating 3-D geomechanical models &ndash a case study for a gas reservoir in the North German Basin." Solid Earth 4, no. 2 (October 15, 2013): 347–55. http://dx.doi.org/10.5194/se-4-347-2013.
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Abstract. The optimal use of conventional and unconventional hydrocarbon reservoirs depends, amongst other things, on the local tectonic stress field. For example, wellbore stability, orientation of hydraulically induced fractures and – especially in fractured reservoirs – permeability anisotropies are controlled by the present-day in situ stresses. Faults and lithological changes can lead to stress perturbations and produce local stresses that can significantly deviate from the regional stress field. Geomechanical reservoir models aim for a robust, ideally "pre-drilling" prediction of the local variations in stress magnitude and orientation. This requires a numerical modelling approach that is capable to incorporate the specific geometry and mechanical properties of the subsurface reservoir. The workflow presented in this paper can be used to build 3-D geomechanical models based on the finite element (FE) method and ranging from field-scale models to smaller, detailed submodels of individual fault blocks. The approach is successfully applied to an intensively faulted gas reservoir in the North German Basin. The in situ stresses predicted by the geomechanical FE model were calibrated against stress data actually observed, e.g. borehole breakouts and extended leak-off tests. Such a validated model can provide insights into the stress perturbations in the inter-well space and undrilled parts of the reservoir. In addition, the tendency of the existing fault network to slip or dilate in the present-day stress regime can be addressed.
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Zhan, Weichen, Mingwei Zhuang, Qi Qiang Liu, Linlin Shi, Yuefeng Sun, and Qing Huo Liu. "Frequency domain spectral element method for modelling poroelastic waves in 3-D anisotropic, heterogeneous and attenuative porous media." Geophysical Journal International 227, no. 2 (July 15, 2021): 1339–53. http://dx.doi.org/10.1093/gji/ggab269.
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SUMMARY Simulating poroelastic waves in large-scale 3-D problems having porous media coupled with elastic solids and fluids is computationally challenging for traditional methods. It is well established that the spectral element method (SEM) is more effective than the traditional methods like the finite element method (FEM) when dealing with complex geophysical problems, for its high-order accuracy with exponential convergence. However, at present, little research has been done for SEM in the frequency domain, which will be more efficient than the time-domain SEM for narrowband simulations with multiple sources, material dispersion and attenuation. Herein, we systematically develop a SEM in the frequency domain to simulate coupled poroelastic, elastic and acoustic waves in anisotropic (i.e. porosity, permeability and elastic coefficients with anisotropy), heterogeneous, and lossy media. Furthermore, we completely remove the dimension inconsistency between the displacement field and the pressure in porous media to reduce the condition number of the system matrix by around 16 orders of magnitude while maintaining the symmetry of the system matrix. To solve the multiphysics coupling problems, we apply different coupling conditions to different interface types, and use basis functions to discretize the corresponding governing equations. Numerical examples show that the proposed SEM can obtain higher accuracy with much fewer unknowns compared with the FEM and has the capacity to solve the large-scale real coupling problems.
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Federico, S. "Implementation of a 3-D-Var system for atmospheric profiling data assimilation into the RAMS model: initial results." Atmospheric Measurement Techniques Discussions 6, no. 2 (April 12, 2013): 3581–610. http://dx.doi.org/10.5194/amtd-6-3581-2013.
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Abstract. This paper presents the current status of development of a three-dimensional variational data assimilation system. The system can be used with different numerical weather prediction models, but it is mainly designed to be coupled with the Regional Atmospheric Modelling System (RAMS). Analyses are given for the following parameters: zonal and meridional wind components, temperature, relative humidity, and geopotential height. Important features of the data assimilation system are the use of incremental formulation of the cost-function, and the use of an analysis space represented by recursive filters and eigenmodes of the vertical background error matrix. This matrix and the length-scale of the recursive filters are estimated by the National Meteorological Center (NMC) method. The data assimilation and forecasting system is applied to the real context of atmospheric profiling data assimilation, and in particular to the short-term wind prediction. The analyses are produced at 20 km horizontal resolution over central Europe and extend over the whole troposphere. Assimilated data are vertical soundings of wind, temperature, and relative humidity from radiosondes, and wind measurements of the European wind profiler network. Results show the validity of the analysis solutions because they are closer to the observations (lower RMSE) compared to the background (higher RMSE), and the differences of the RMSEs are consistent with the data assimilation settings. To quantify the impact of improved initial conditions on the short-term forecast, the analyses are used as initial conditions of a three-hours forecast of the RAMS model. In particular two sets of forecasts are produced: (a) the first uses the ECMWF analysis/forecast cycle as initial and boundary conditions; (b) the second uses the analyses produced by the 3-D-Var scheme as initial conditions, then is driven by the ECMWF forecast. The improvement is quantified by considering the horizontal components of the wind, which are measured at a-synoptic times by the European wind profiler network. The results show that the RMSE is effectively reduced at the short range (1–2 h). The results are in agreement with the set-up of the numerical experiment.
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Chen, Xuelong, Bojan Škerlak, Mathias W. Rotach, Juan A. Añel, Zhonbgo Su, Yaoming Ma, and Maoshan Li. "Reasons for the Extremely High-Ranging Planetary Boundary Layer over the Western Tibetan Plateau in Winter." Journal of the Atmospheric Sciences 73, no. 5 (April 22, 2016): 2021–38. http://dx.doi.org/10.1175/jas-d-15-0148.1.
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Abstract The planetary boundary layer (PBL) over the Tibetan Plateau (with a mean elevation about 4 km above sea level) reaches an unmatched height of 9515 m above sea level. The proximity of this height to the tropopause facilitates an exchange between the stratosphere and the boundary layer. However, the underlying mechanisms responsible for this unique PBL have remained uncertain. Here, the authors explore these mechanisms and their relative importance using measurements of the PBL, the associated surface fluxes, and single-column and regional numerical simulations, as well as global reanalysis data. Results indicate that the dry conditions of both ground soil and atmosphere in late winter cannot explain the special PBL alone. Rather, the results from a single-column model demonstrate the key influence of the stability of the free atmosphere upon the growth of extremely deep PBLs over the Tibetan Plateau. Simulations with the numerical weather prediction model Consortium for Small-Scale Modelling (COSMO) exhibit good correspondence with the observed mean PBL structure and realistic turbulent kinetic energy distributions throughout the PBL. Using ERA-Interim, the authors furthermore find that weak atmospheric stability and the resultant deep PBLs are associated with higher upper-level potential vorticity (PV) values, which in turn correspond to a more southerly jet position and higher wind speeds. Upper-level PV structures and jet position thus influence the PBL development over the Tibetan Plateau.
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Fiddes, J., and S. Gruber. "TopoSUB: a tool for efficient large area numerical modelling in complex topography at sub-grid scales." Geoscientific Model Development 5, no. 5 (October 10, 2012): 1245–57. http://dx.doi.org/10.5194/gmd-5-1245-2012.
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Abstract. Mountain regions are highly sensitive to global climate change. However, large scale assessments of mountain environments remain problematic due to the high resolution required of model grids to capture strong lateral variability. To alleviate this, tools are required to bridge the scale gap between gridded climate datasets (climate models and re-analyses) and mountain topography. We address this problem with a sub-grid method. It relies on sampling the most important aspects of land surface heterogeneity through a lumped scheme, allowing for the application of numerical land surface models (LSMs) over large areas in mountain regions or other heterogeneous environments. This is achieved by including the effect of mountain topography on these processes at the sub-grid scale using a multidimensional informed sampling procedure together with a 1-D lumped model that can be driven by gridded climate datasets. This paper provides a description of this sub-grid scheme, TopoSUB, and assesses its performance against a distributed model. We demonstrate the ability of TopoSUB to approximate results simulated by a distributed numerical LSM at around 104 less computations. These significant gains in computing resources allow for: (1) numerical modelling of processes at fine grid resolutions over large areas; (2) efficient statistical descriptions of sub-grid behaviour; (3) a "sub-grid aware" aggregation of simulated variables to coarse grids; and (4) freeing of resources for computationally intensive tasks, e.g., the treatment of uncertainty in the modelling process.
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Fiddes, J., and S. Gruber. "TopoSUB: a tool for efficient large area numerical modelling in complex topography at sub-grid scales." Geoscientific Model Development Discussions 5, no. 2 (May 2, 2012): 1041–76. http://dx.doi.org/10.5194/gmdd-5-1041-2012.
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Abstract. Mountain regions are highly sensitive to global climate change. However, large scale assessments of mountain environments remain problematic due to the high resolution required of model grids to capture strong lateral variability. To alleviate this, tools are required to bridge the scale gap between gridded climate datasets (climate models and re-analyses) and unresolved (by coarse grids) sub-grid mountain topography. We address this problem with a sub-grid method. It relies on sampling the most important aspects of land surface heterogeneity through a lumped scheme, allowing for the application of numerical land surface models (LSM) over large areas in mountain regions. This is achieved by including the effect of mountain topography on these processes at the sub-grid scale using a multidimensional informed sampling procedure together with a 1-D lumped model that can be driven by gridded climate datasets. This paper provides a description of this sub-grid scheme, TopoSUB, as well as assessing its performance against a distributed model. We demonstrate the ability of TopoSUB to approximate results simulated by a distributed numerical LSM at around 104 less computations. These significant gains in computing resources allow for: (1) numerical modelling of processes at fine grid resolutions over large areas; (2) extremely efficient statistical descriptions of sub-grid behaviour; (3) a "sub-grid aware" aggregation of simulated variables to course grids; and (4) freeing of resources for treatment of uncertainty in the modelling process.
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Lashgari, Katarina, Anders Moberg, and Gudrun Brattström. "Evaluation of simulated responses to climate forcings: a flexible statistical framework using confirmatory factor analysis and structural equation modelling – Part 2: Numerical experiment." Advances in Statistical Climatology, Meteorology and Oceanography 8, no. 2 (December 14, 2022): 249–71. http://dx.doi.org/10.5194/ascmo-8-249-2022.
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Abstract. The performance of a new statistical framework, developed for the evaluation of simulated temperature responses to climate forcings against temperature reconstructions derived from climate proxy data for the last millennium, is evaluated in a so-called pseudo-proxy experiment, where the true unobservable temperature is replaced with output data from a selected simulation with a climate model. Being an extension of the statistical model used in many detection and attribution (D&A) studies, the framework under study involves two main types of statistical models, each of which is based on the concept of latent (unobservable) variables: confirmatory factor analysis (CFA) models and structural equation modelling (SEM) models. Within the present pseudo-proxy experiment, each statistical model was fitted to seven continental-scale regional data sets. In addition, their performance for each defined region was compared to the performance of the corresponding statistical model used in D&A studies. The results of this experiment indicated that the SEM specification is the most appropriate one for describing the underlying latent structure of the simulated temperature data in question. The conclusions of the experiment have been confirmed in a cross-validation study, presuming the availability of several simulation data sets within each studied region. Since the experiment is performed only for zero noise level in the pseudo-proxy data, all statistical models, chosen as final regional models, await further investigation to thoroughly test their performance for realistic levels of added noise, similar to what is found in real proxy data for past temperature variations.
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Nikolov, N., T. Avdjieva, and I. Altaparmakov. "Length-Scale Effects and Material Models at Numerical Simulations of Nanoindentation of A Metallic Alloy." Journal of Theoretical and Applied Mechanics 44, no. 2 (June 1, 2014): 25–40. http://dx.doi.org/10.2478/jtam-2014-0008.
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Abstract Some specially designed metallic alloys crystallize during process of rapid quenching which aims their amorphization. Nevertheless, change in their mechanical properties could be seen compared to these obtained during conventional technological regimes of cooling. That attracts the attention in this elaboration. Full 3-D numerical simulations of nanoindentation process of two material models are performed. The models reflect equivalent elastic and different plastic material properties. The plastic behaviour of the first one is subjected to yield criterion of Dracker-Prager and this of the second one to yield criterion of Mises. The reported numerical results depending on the nanoindentation scale length of 1000 nanometers, suggest different adequacy of the two yield criteria to the data obtained experimentally with a Zr-Al-Cu-Ni-Mo alloy. It could be speculated that the different effects developed depending on the indenter travel of 1000 nanometers and taken into account in the two yield criteria stand behind this fact and determinate three structural levels of plastic deformation.
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Lin, Chuangxin, Vadim Monteiller, Kai Wang, Tianshi Liu, Ping Tong, and Qinya Liu. "High-frequency seismic wave modelling of the deep Earth based on hybrid methods and spectral-element simulations: a conceptual study." Geophysical Journal International 219, no. 3 (September 12, 2019): 1948–69. http://dx.doi.org/10.1093/gji/ggz413.
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SUMMARY Over the past few decades, seismic studies have revealed complex structural anomalies in the Earth’s deep interior at various scales, such as large low-shear-velocity provinces (LLSVPs) and ultra-low velocity zones (ULVZs) in the lowermost mantle, and small-scale scatterers in the mid-mantle. These structures which are critical for better understanding of the geodynamics and evolution of the deep Earth, need to be further resolved by high-resolution imaging techniques. The spectral-element method (SEM) can be used to accurately simulate seismic wave propagation in heterogeneous Earth models, and its application in full-waveform inversion (FWI) provides a promising high-resolution and high-fidelity imaging technique. But it can be computationally prohibitive when used to model small scale structures in the deep Earth based upon high-frequency seismic waves. The heavy computational cost can be circumvented by using hybrid methods, which restrict the main computation by SEM solver to only a small target region (e.g. above the CMB) encompassing possible 2-D/3-D anomalies, and apply efficient analytical or numerical methods to calculate the wavefield for 1-D background models. These forward modelling tools based on hybrid methods can be then used in the so-called ‘box tomography’ approach to resolve fine-structures in the deep Earth. In this study, we outline the theory of a hybrid method used to model small scale structures in the deep Earth and present its implementation based on SEM solvers in a three-step workflow. First, the wavefield generated by the source is computed for the 1-D background model with traction and velocity saved for the virtual boundary of the target region, which are then used as boundary inputs to simulate the wavefield in the target region based on absorbing boundary condition in SEM. In the final step, the total wavefield at receivers is reconstructed based upon the total wavefield on the virtual boundary computed in the previous step. As a proof-of-concept study, we demonstrate the workflow of the hybrid method based on a 2-D SEM solver. Examples of the hybrid method applied to a coupled fluid–solid model show that our workflow can accurately recover the scattered waves back to the surface. Furthermore, we benchmark the hybrid method on a realistic heterogeneous Earth model built from AK135-F and show how teleseismic scattered waves can be used to model deep Earth structures. By documenting the theory and SEM implementation of the hybrid method, our study lays the foundation for future two-way coupling of 3-D SEM solver with other efficient analytic or numerical 1-D solvers.
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Manassero, M. C., J. C. Afonso, F. Zyserman, S. Zlotnik, and I. Fomin. "A reduced order approach for probabilistic inversions of 3-D magnetotelluric data I: general formulation." Geophysical Journal International 223, no. 3 (September 1, 2020): 1837–63. http://dx.doi.org/10.1093/gji/ggaa415.
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SUMMARY Simulation-based probabilistic inversions of 3-D magnetotelluric (MT) data are arguably the best option to deal with the nonlinearity and non-uniqueness of the MT problem. However, the computational cost associated with the modelling of 3-D MT data has so far precluded the community from adopting and/or pursuing full probabilistic inversions of large MT data sets. In this contribution, we present a novel and general inversion framework, driven by Markov Chain Monte Carlo (MCMC) algorithms, which combines (i) an efficient parallel-in-parallel structure to solve the 3-D forward problem, (ii) a reduced order technique to create fast and accurate surrogate models of the forward problem and (iii) adaptive strategies for both the MCMC algorithm and the surrogate model. In particular, and contrary to traditional implementations, the adaptation of the surrogate is integrated into the MCMC inversion. This circumvents the need of costly offline stages to build the surrogate and further increases the overall efficiency of the method. We demonstrate the feasibility and performance of our approach to invert for large-scale conductivity structures with two numerical examples using different parametrizations and dimensionalities. In both cases, we report staggering gains in computational efficiency compared to traditional MCMC implementations. Our method finally removes the main bottleneck of probabilistic inversions of 3-D MT data and opens up new opportunities for both stand-alone MT inversions and multi-observable joint inversions for the physical state of the Earth’s interior.
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Takemura, Shunsuke, Suguru Yabe, and Kentaro Emoto. "Modelling high-frequency seismograms at ocean bottom seismometers: effects of heterogeneous structures on source parameter estimation for small offshore earthquakes and shallow low-frequency tremors." Geophysical Journal International 223, no. 3 (August 26, 2020): 1708–23. http://dx.doi.org/10.1093/gji/ggaa404.
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SUMMARY The source characteristics of offshore seismic events, especially regular (or fast) and slow earthquakes, can provide key information on their source physics and frictional conditions at the plate boundary. Due to strong 3-D heterogeneities in offshore regions, such as those relating to sea water, accretionary prism and small-scale velocity heterogeneity, conventional methods using a 1-D earth model may mis-estimate source parameters such as the duration and radiation energy. Estimations could become severe inaccuracies for small offshore seismic events because high-frequency (>1 Hz) seismograms, which are strongly affected by 3-D heterogeneities, are only available for analysis because of their signal-to-noise ratio. To investigate the effects of offshore heterogeneities on source parameter estimation for small seismic events, we analysed both observed and simulated high-frequency seismograms southeast off the Kii Peninsula, Japan, in the Nankai subduction zone. Numerical simulations of seismic wave propagation using a 3-D velocity structure model clarified the effects of each heterogeneity. Comparisons between observations and model simulations demonstrated that the thick low-velocity accretionary prism has significant effects on high-frequency seismic wave propagation. Especially for shallow low-frequency tremors occurring at depths just below the accretionary prism toe, seismogram durations are significantly broader than an assumed source duration, even for stations with epicentral distances of approximately 10 km. Spindle-shape seismogram envelopes were observed even at such close stations. Our results suggest that incorporating 3-D heterogeneities is necessary for practical estimation of source parameters for small offshore events.
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Hergert, T., O. Heidbach, K. Reiter, S. B. Giger, and P. Marschall. "Stress field sensitivity analysis in a sedimentary sequence of the Alpine foreland, Northern Switzerland." Solid Earth Discussions 7, no. 1 (February 19, 2015): 711–56. http://dx.doi.org/10.5194/sed-7-711-2015.
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Abstract. The stress field at depth is a relevant parameter for the design of subsurface constructions and reservoir management. Yet the distortion of the regional stress field due to local-scale features such as sedimentary and tectonic structures or topography is often poorly constrained. We conduct a stress sensitivity analysis using 3-D numerical geomechanical modelling with an elasto-plastic material law to explore the impact of such site specific features on the stress field in a sedimentary sequence of the Swiss Alpine foreland. The model's dimensions are 14 km × 14 km × 3 km and it contains ten units with different mechanical properties, intersected by two regional fault zones. An initial stress state is established involving a semi-empirical relationship between the ratio of horizontal to vertical stress and the overconsolidation ratio of argillaceous sediments. The model results indicate that local topography can affect the stress field significantly to depths greater than the relief contrasts at the surface, especially in conjunction with horizontal tectonic loading. The complexity and frictional properties of faults are also relevant. The greatest variability of the stress field arises across the different sedimentary units. Stress magnitudes and stress anisotropy are much larger in stiffer formations such as massive limestones than in softer argillaceous formations. The stiffer formations essentially carry the load of the far-field forces and are therefore more sensitive to changes of the boundary conditions. This general characteristic of stress distribution in the stiff and soft formations is broadly maintained also with progressive loading towards the plastic limit. The stress field in argillaceous sediments within a stack of formations with strongly contrasting mechanical properties like in the Alpine foreland appears to be relatively insensitive to changes in the tectonic boundary conditions and is largely controlled by the maximum stiffness contrast with respect to the load-bearing formations.
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Hergert, T., O. Heidbach, K. Reiter, S. B. Giger, and P. Marschall. "Stress field sensitivity analysis in a sedimentary sequence of the Alpine foreland, northern Switzerland." Solid Earth 6, no. 2 (May 21, 2015): 533–52. http://dx.doi.org/10.5194/se-6-533-2015.
Full textAbstract:
Abstract. The stress field at depth is a relevant parameter for the design of subsurface constructions and reservoir management. Yet the distortion of the regional stress field due to local-scale features such as sedimentary and tectonic structures or topography is often poorly constrained. We conduct a stress sensitivity analysis using 3-D numerical geomechanical modelling with an elasto-plastic material law to explore the impact of such site-specific features on the stress field in a sedimentary sequence of the Swiss Alpine foreland. The model's dimensions are 14 × 14 × 3 km3 and it contains 10 units with different mechanical properties, intersected by two regional fault zones. An initial stress state is established involving a semi-empirical relationship between the ratio of horizontal to vertical stress and the overconsolidation ratio of argillaceous sediments. The model results indicate that local topography can affect the stress field significantly to depths greater than the relief contrasts at the surface, especially in conjunction with horizontal tectonic loading. The complexity and frictional properties of faults are also relevant. The greatest variability of the stress field arises across the different sedimentary units. Stress magnitudes and stress anisotropy are much larger in stiffer formations such as massive limestones than in softer argillaceous formations. The stiffer formations essentially carry the load of the far-field forces and are therefore more sensitive to changes of the boundary conditions. This general characteristic of stress distribution in the stiff and soft formations is broadly maintained also with progressive loading towards the plastic limit. The stress field in argillaceous sediments within a stack of formations with strongly contrasting mechanical properties like in the Alpine foreland appears to be relatively insensitive to changes in the tectonic boundary conditions and is largely controlled by the maximum stiffness contrast with respect to the load-bearing formations.
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Ayache, M., J. C. Dutay, P. Jean-Baptiste, K. Beranger, T. Arsouze, J. Beuvier, J. Palmieri, B. Le-vu, and W. Roether. "Modelling of the anthropogenic tritium transient and its decay product helium-3 in the Mediterranean Sea using a high-resolution regional model." Ocean Science 11, no. 3 (May 12, 2015): 323–42. http://dx.doi.org/10.5194/os-11-323-2015.
Full textAbstract:
Abstract. This numerical study provides the first simulation of the anthropogenic tritium invasion and its decay product helium-3 (3He) in the Mediterranean Sea. The simulation covers the entire tritium (3H) transient generated by the atmospheric nuclear weapons tests performed in the 1950s and early 1960s and is run till 2011. Tritium, helium-3 and their derived age estimates are particularly suitable for studying intermediate and deep-water ventilation and spreading of water masses at intermediate/deep levels. The simulation is made using a high-resolution regional model NEMO (Nucleus for European Modelling of the Ocean), in a regional configuration for the Mediterranean Sea called MED12, forced at the surface with prescribed tritium evolution derived from observations. The simulation is compared to measurements of tritium and helium-3 performed along large-scale transects in the Mediterranean Sea during the last few decades on cruises of R/V Meteor: M5/6, M31/1, M44/4, M51/2, M84/3, and R/V Poseidon: 234. The results show that the input function used for the tritium generates a realistic distribution of the main hydrographic features of the Mediterranean Sea circulation. In the eastern basin, the results highlight the weak formation of Adriatic Deep Water in the model, which explains its weak contribution to the Eastern Mediterranean Deep Water (EMDW) in the Ionian sub-basin. It produces a realistic representation of the Eastern Mediterranean Transient (EMT) signal, simulating a deep-water formation in the Aegean sub-basin at the beginning of 1993, with a realistic timing of deep-water renewal in the eastern basin.
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Perrier, E. M. A., N. R. A. Bird, and T. B. Rieutord. "Percolation properties of 3-D multiscale pore networks: how connectivity controls soil filtration processes." Biogeosciences Discussions 7, no. 2 (April 27, 2010): 2997–3018. http://dx.doi.org/10.5194/bgd-7-2997-2010.
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Abstract. Quantifying the connectivity of pore networks is a key issue not only for modelling fluid flow and solute transport in porous media but also for assessing the ability of soil ecosystems to filter bacteria, viruses and any type of living microorganisms as well inert particles which pose a contamination risk. Straining is the main mechanical component of filtration processes: it is due to size effects, when a given soil retains a conveyed entity larger than the pores through which it is attempting to pass. We postulate that the range of sizes of entities which can be trapped inside soils has to be associated with the large range of scales involved in natural soil structures and that information on the pore size distribution has to be complemented by information on a Critical Filtration Size (CFS) delimiting the transition between percolating and non percolating regimes in multiscale pore networks. We show that the mass fractal dimensions which are classically used in soil science to quantify scaling laws in observed pore size distributions can also be used to build 3-D multiscale models of pore networks exhibiting such a critical transition. We extend to the 3-D case a new theoretical approach recently developed to address the connectivity of 2-D fractal networks (Bird and Perrier, 2009). Theoretical arguments based on renormalisation functions provide insight into multi-scale connectivity and a first estimation of CFS. Numerical experiments on 3-D prefractal media confirm the qualitative theory. These results open the way towards a new methodology to estimate soil filtration efficiency from the construction of soil structural models to be calibrated on available multiscale data.
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Perrier, E. M. A., N. R. A. Bird, and T. B. Rieutord. "Percolation properties of 3-D multiscale pore networks: how connectivity controls soil filtration processes." Biogeosciences 7, no. 10 (October 18, 2010): 3177–86. http://dx.doi.org/10.5194/bg-7-3177-2010.
Full textAbstract:
Abstract. Quantifying the connectivity of pore networks is a key issue not only for modelling fluid flow and solute transport in porous media but also for assessing the ability of soil ecosystems to filter bacteria, viruses and any type of living microorganisms as well inert particles which pose a contamination risk. Straining is the main mechanical component of filtration processes: it is due to size effects, when a given soil retains a conveyed entity larger than the pores through which it is attempting to pass. We postulate that the range of sizes of entities which can be trapped inside soils has to be associated with the large range of scales involved in natural soil structures and that information on the pore size distribution has to be complemented by information on a critical filtration size (CFS) delimiting the transition between percolating and non percolating regimes in multiscale pore networks. We show that the mass fractal dimensions which are classically used in soil science to quantify scaling laws in observed pore size distributions can also be used to build 3-D multiscale models of pore networks exhibiting such a critical transition. We extend to the 3-D case a new theoretical approach recently developed to address the connectivity of 2-D fractal networks (Bird and Perrier, 2009). Theoretical arguments based on renormalisation functions provide insight into multi-scale connectivity and a first estimation of CFS. Numerical experiments on 3-D prefractal media confirm the qualitative theory. These results open the way towards a new methodology to estimate soil filtration efficiency from the construction of soil structural models to be calibrated on available multiscale data.
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Xu, Lei, and Wanming Zhai. "Vehicle–track–tunnel dynamic interaction: a finite/infinite element modelling method." Railway Engineering Science 29, no. 2 (June 2021): 109–26. http://dx.doi.org/10.1007/s40534-021-00238-x.
Full textAbstract:
AbstractThe aim of this study is to develop coupled matrix formulations to characterize the dynamic interaction between the vehicle, track, and tunnel. The vehicle–track coupled system is established in light of vehicle–track coupled dynamics theory. The physical characteristics and mechanical behavior of tunnel segments and rings are modeled by the finite element method, while the soil layers of the vehicle–track–tunnel (VTT) system are modeled as an assemblage of 3-D mapping infinite elements by satisfying the boundary conditions at the infinite area. With novelty, the tunnel components, such as rings and segments, have been coupled to the vehicle–track systems using a matrix coupling method for finite elements. The responses of sub-systems included in the VTT interaction are obtained simultaneously to guarantee the solution accuracy. To relieve the computer storage and save the CPU time for the large-scale VTT dynamics system with high degrees of freedoms, a cyclic calculation method is introduced. Apart from model validations, the necessity of considering the tunnel substructures such as rings and segments is demonstrated. In addition, the maximum number of elements in the tunnel segment is confirmed by numerical simulations.
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Haapala, Jari. "On the modelling of ice-thickness redistribution." Journal of Glaciology 46, no. 154 (2000): 427–37. http://dx.doi.org/10.3189/172756500781833106.
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AbstractAn ice-thickness distribution model based on physical ice classes is formulated. Pack ice is subdivided into open water, two different types of undeformed ice, and rafted, rubble and ridged ice. Evolution equations for each ice class are formulated and a redistribution between the ice classes is calculated according to a functional form depending on the ice compactness, thickness and velocity divergence. The ice-thickness distribution model has been included in a coupled ice–ocean model, and numerical experiments have been carried out for a simulation of the Baltic Sea ice season. The extended ice classification allows separation of thermally and mechanically produced ice. Inherent thermodynamic growth/melting rates of the ice classes can be introduced into the model, giving a more detailed seasonal evolution of the pack ice. In addition, the model provides more information about the surface properties of pack ice.Numerical experiments for the Baltic Sea show that both the sub-basin and inter-basin ice characteristics were realistically simulated by the model. Deformed-ice production was related to storm activity. Most of the deformation was produced in the coastal zone, which is also an important region for thermodynamically produced ice because of the ice growth in leads. The modelled mechanical growth rates of ice were 0.5–3 cm d−1 on a basin scale, close to the thermodynamic ice-production rates. The deformed-ice fraction was 0.2 in mid-winter and increased to 0.5–1.0 during spring.
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Tian, Zhiping, Tim Li, and Dabang Jiang. "Strengthening and Westward Shift of the Tropical Pacific Walker Circulation during the Mid-Holocene: PMIP Simulation Results." Journal of Climate 31, no. 6 (March 2018): 2283–98. http://dx.doi.org/10.1175/jcli-d-16-0744.1.
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Based on the zonal mass streamfunction, the mid-Holocene annual and seasonal changes in the tropical Pacific Walker circulation (PWC) are examined using numerical simulations from the Paleoclimate Modelling Intercomparison Project Phases 2 and 3. Compared to the preindustrial period, the annual mean of the PWC intensity strengthened (with an average increase of 0.26 × 1014 kg2 m−2 s−1 or 5%), and both the western edge and center of the PWC cell shifted westward (by an average of 4° and 3°, respectively) in the majority of the 29 models used for analysis during the mid-Holocene. Those changes were closely related to an overall increase in the equatorial Indo-Pacific east–west sea level pressure difference and low-level trade winds over the equatorial Pacific. Annual mean PWC changes come mainly from boreal warm seasons. In response to the mid-Holocene orbital forcing, Asian and North African monsoon rainfall was strengthened due to large-scale surface warming in the Northern Hemisphere in boreal warm seasons, which led to an intensified large-scale thermally direct east–west circulation, resulting in the enhancement and westward shift of the tropical PWC. The opposite occurred during the mid-Holocene boreal cold seasons. Taken together, the change in the monsoon rainfall over the key tropical regions of Asia and North Africa and associated large-scale east–west circulation, rather than the equatorial Pacific SST change pattern, played a key role in affecting the mid-Holocene PWC strength.
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Dabrowski, T., K. Lyons, C. Cusack, G. Casal, A. Berry, and G. D. Nolan. "Ocean modelling for aquaculture and fisheries in Irish waters." Ocean Science Discussions 12, no. 3 (June 25, 2015): 1187–217. http://dx.doi.org/10.5194/osd-12-1187-2015.
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Abstract. The Marine Institute, Ireland, runs a suite of operational regional and coastal ocean models. Recent developments include several tailored products that focus on the key needs of the Irish aquaculture sector. In this article, an overview of the products and services derived from the models are presented. A shellfish model that includes growth and physiological interactions of mussels with the ecosystem and is fully embedded in the 3-D numerical modelling framework has been developed at the Marine Institute. This shellfish model has a microbial module designed to predict levels of coliform contamination in mussels. This model can also be used to estimate the carrying capacity of embayments, assess impacts of pollution on aquaculture grounds and help to classify shellfish waters. The physical coastal model of southwest Ireland provides a three day forecast of shelf water movement in the region. This is assimilated into a new harmful algal bloom alert system used to inform end-users of potential toxic shellfish events and high biomass blooms that include fish killing species. Further services include the use of models to identify potential sites for offshore aquaculture, to inform studies of potential cross-contamination in farms from the dispersal of planktonic sea lice larvae and other pathogens that can infect finfish and to provide modelled products that underpin the assessment and advisory services on the sustainable exploitation of the marine fisheries resources. This paper demonstrates that ocean models can provide an invaluable contribution to the sustainable blue growth of aquaculture and fisheries.
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Redzuan, Faisal Amsyar. "Partial Strength Beam-to-column Connection of Cold-formed Single Channel Section: Numerical and Experimental Study." ASM Science Journal 14 (April 5, 2021): 1–11. http://dx.doi.org/10.32802/asmscj.2020.639.
Full textAbstract:
A full understanding of complex structural behaviour can be developed perfectly by using the combination of experimental and numerical approach. Although the basic method to determine the moment-rotation responses of the beam-to-column CFS joints has recently established from the full-scale testing, practising the finite element modelling (FEM) nowadays could explore in-depth on the number of variables and potential failure modes. In this paper, three-dimensional (3-D) model to simulate the actual behaviour of the beam-to-column CFS joints has been proposed by using multi-purpose finite element package ABAQUS version 6.14 in order to validate analysis data against the experimental works. The approach of nonlinear material characteristics, contact and sliding between different components and adopting C3D8R solid elements are proposed in this model. A total of three (3) beam-to-column CFS connections consisting of three different types of beam depths were tested in isolation in order to observe the structural behaviour based on its strength and stiffness. Comparisons between experimental and FE analysis results in term of ultimate moment capacity have shown a good correlation with strength ratios ranging from 1.12 to 1.17. Therefore, it is possible to develop a realistic model for future parametric studies such as type and configurations of the connections.
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Tenzer, Robert, Yuting Ji, and Wenjin Chen. "The Accuracy Assessment of the PREM and AK135-F Radial Density Models." Sensors 22, no. 11 (May 31, 2022): 4180. http://dx.doi.org/10.3390/s22114180.
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The Earth’s synthetic density and gravitational models can be used to validate numerical methods for global (or large-scale) gravimetric forward and inverse modelling formulated either in the spatial or spectral domains. The Preliminary Reference Earth Model (PREM) density parameters can be adopted as a 1-D reference density model and further refined using more detailed 2-D or 3-D crust and mantle density models. Alternatively, the AK135-F density parameters can be used for this purpose. In this study, we investigate options for a refinement of the Earth’s synthetic density model by assessing the accuracy of available 1-D density models, specifically the PREM and AK135-F radial density parameters. First, we use density parameters from both models to estimate the Earth’s total mass and compare these estimates with published results. We then estimate the Earth’s gravity field parameters, particularly the geoidal geopotential number W0 and the mean gravitational attraction and compare them with published values. According to our results, the Earth’s total mass from the two models (the PREM and the AK135-F) differ less than 0.02% and 0.01%, respectively, when compared with the value adopted by the International Astronomical Union (IAU). The geoidal geopotential values of the two models differ from the value adopted by the IAU by less than 0.1% and 0.04%, respectively. The values of the mean gravitational attraction of the two models differ less than 0.02% and 0.08%, respectively, when compared with the value obtained from the geocentric gravitational constant and the Earth’s mean radius. These numerical findings ascertain that the PREM and AK135-F density parameters are suitable for defining a 1-D reference density model.
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Zoccarato, Claudia, Laura Gazzola, Massimiliano Ferronato, and Pietro Teatini. "Generalized Polynomial Chaos Expansion for Fast and Accurate Uncertainty Quantification in Geomechanical Modelling." Algorithms 13, no. 7 (June 30, 2020): 156. http://dx.doi.org/10.3390/a13070156.
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Geomechanical modelling of the processes associated to the exploitation of subsurface resources, such as land subsidence or triggered/induced seismicity, is a common practice of major interest. The prediction reliability depends on different sources of uncertainty, such as the parameterization of the constitutive model characterizing the deep rock behaviour. In this study, we focus on a Sobol’-based sensitivity analysis and uncertainty reduction via assimilation of land deformations. A synthetic test case application on a deep hydrocarbon reservoir is considered, where land settlements are predicted with the aid of a 3-D Finite Element (FE) model. Data assimilation is performed via the Ensemble Smoother (ES) technique and its variation in the form of Multiple Data Assimilation (ES-MDA). However, the ES convergence is guaranteed with a large number of Monte Carlo (MC) simulations, that may be computationally infeasible in large scale and complex systems. For this reason, a surrogate model based on the generalized Polynomial Chaos Expansion (gPCE) is proposed as an approximation of the forward problem. This approach allows to efficiently compute the Sobol’ indices for the sensitivity analysis and greatly reduce the computational cost of the original ES and MDA formulations, also enhancing the accuracy of the overall prediction process.
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Persing, J., M. T. Montgomery, J. C. McWilliams, and R. K. Smith. "Asymmetric and axisymmetric dynamics of tropical cyclones." Atmospheric Chemistry and Physics Discussions 13, no. 5 (May 22, 2013): 13323–438. http://dx.doi.org/10.5194/acpd-13-13323-2013.
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Abstract. We present the results of idealized numerical experiments to examine the difference between tropical cyclone evolution in three-dimensional (3-D) and axisymmetric (AX) model configurations. We focus on the prototype problem for intensification, which considers the evolution of an initially unsaturated AX vortex in gradient-wind balance on an f-plane. Consistent with findings of previous work, the mature intensity in the 3-D model is reduced relative to that in the AX model. In contrast with previous interpretations invoking barotropic instability and related horizontal mixing processes as a mechanism detrimental to the spin-up process, the results indicate that 3-D eddy processes associated with vortical plume structures can assist the intensification process by contributing to a radial contraction of the maximum tangential velocity and to a vertical extension of tangential winds through the depth of the troposphere. These plumes contribute significantly also to the azimuthally-averaged heating rate and the corresponding azimuthal-mean overturning circulation. The comparisons show that the resolved 3-D eddy momentum fluxes above the boundary layer exhibit counter-gradient characteristics and are generally not represented properly by the subgrid-scale parameterizations in the AX configuration. The resolved eddy fluxes act to support the contraction and intensification of the maximum tangential winds. The comparisons indicate fundamental differences between convective organization in the 3-D and AX configurations for meteorologically relevant forecast time scales. While the radial and vertical gradients of the system-scale angular rotation provide a hostile environment for deep convection in the 3-D model, with a corresponding tendency to strain the convective elements in the tangential direction, deep convection in the AX model does not suffer this tendency. Also, since during the 3-D intensification process the convection has not yet organized into annular rings, the azimuthally-averaged heating rate and radial gradient thereof is considerably less than that in the AX model. This lack of organization results broadly in a slower intensification rate in the 3-D model and leads ultimately to a weaker mature vortex after 12 days of model integration. While axisymmetric heating rates in the 3-D model are weaker than those in the AX model, local heating rates in the 3-D model exceed those in the AX model and at times the vortex in the 3-D model intensifies more rapidly than AX. Analyses of the 3-D model output do not support a recent hypothesis concerning the key role of small-scale vertical mixing processes in the upper-tropospheric outflow in controlling the intensification process. In the 3-D model, surface drag plays a particularly important role in the intensification process for the prototype intensification problem on meteorologically relevant time scales by helping foster the organization of convection in azimuth. There is a radical difference in the behaviour of the 3-D and AX simulations when the surface drag is reduced or increased from realistic values. Borrowing from ideas developed in a recent paper, we give a partial explanation for this difference in behaviour. Our results provide new qualitative and quantitative insight into the differences between the asymmetric and symmetric dynamics of tropical cyclones and would appear to have important consequences for the formulation of a fluid dynamical theory of tropical cyclone intensification and mature intensity. In particular, the results point to some fundamental limitations of strict axisymmetric theory and modelling for representing the azimuthally-averaged behaviour of tropical cyclones in three dimensions.
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Persing, J., M. T. Montgomery, J. C. McWilliams, and R. K. Smith. "Asymmetric and axisymmetric dynamics of tropical cyclones." Atmospheric Chemistry and Physics 13, no. 24 (December 18, 2013): 12299–341. http://dx.doi.org/10.5194/acp-13-12299-2013.
Full textAbstract:
Abstract. We present the results of idealized numerical experiments to examine the difference between tropical cyclone evolution in three-dimensional (3-D) and axisymmetric (AX) model configurations. We focus on the prototype problem for intensification, which considers the evolution of an initially unsaturated AX vortex in gradient-wind balance on an f plane. Consistent with findings of previous work, the mature intensity in the 3-D model is reduced relative to that in the AX model. In contrast with previous interpretations invoking barotropic instability and related horizontal mixing processes as a mechanism detrimental to the spin-up process, the results indicate that 3-D eddy processes associated with vortical plume structures can assist the intensification process by contributing to a radial contraction of the maximum tangential velocity and to a vertical extension of tangential winds through the depth of the troposphere. These plumes contribute significantly also to the azimuthally averaged heating rate and the corresponding azimuthal-mean overturning circulation. The comparisons show that the resolved 3-D eddy momentum fluxes above the boundary layer exhibit counter-gradient characteristics during a key spin-up period, and more generally are not solely diffusive. The effects of these eddies are thus not properly represented by the subgrid-scale parameterizations in the AX configuration. The resolved eddy fluxes act to support the contraction and intensification of the maximum tangential winds. The comparisons indicate fundamental differences between convective organization in the 3-D and AX configurations for meteorologically relevant forecast timescales. While the radial and vertical gradients of the system-scale angular rotation provide a hostile environment for deep convection in the 3-D model, with a corresponding tendency to strain the convective elements in the tangential direction, deep convection in the AX model does not suffer this tendency. Also, since during the 3-D intensification process the convection has not yet organized into annular rings, the azimuthally averaged heating rate and radial gradient thereof is considerably less than that in the AX model. This lack of organization results broadly in a slower intensification rate in the 3-D model and leads ultimately to a weaker mature vortex after 12 days of model integration. While azimuthal mean heating rates in the 3-D model are weaker than those in the AX model, local heating rates in the 3-D model exceed those in the AX model and at times the vortex in the 3-D model intensifies more rapidly than AX. Analyses of the 3-D model output do not support a recent hypothesis concerning the key role of small-scale vertical mixing processes in the upper-tropospheric outflow in controlling the intensification process. In the 3-D model, surface drag plays a particularly important role in the intensification process for the prototype intensification problem on meteorologically relevant timescales by helping foster the organization of convection in azimuth. There is a radical difference in the behaviour of the 3-D and AX simulations when the surface drag is reduced or increased from realistic values. Borrowing from ideas developed in a recent paper, we give a partial explanation for this difference in behaviour. Our results provide new qualitative and quantitative insight into the differences between the asymmetric and symmetric dynamics of tropical cyclones and would appear to have important consequences for the formulation of a fluid dynamical theory of tropical cyclone intensification and mature intensity. In particular, the results point to some fundamental limitations of strict axisymmetric theory and modelling for representing the azimuthally averaged behaviour of tropical cyclones in three dimensions.