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1.
Mathematical Geosciences - A robust, high order modeling approach is introduced, based on the finite difference-based radial basis functions method, for solving the groundwater flow equation in the...  相似文献   
2.
One important, almost ubiquitous, tool for understanding the surfaces of solid bodies throughout the solar system is the study of impact craters. While measuring a distribution of crater diameters and locations is an important tool for a wide variety of studies, so too is measuring a crater's “depth.” Depth can inform numerous studies including the strength of a surface and modification rates in the local environment. There is, however, no standard data set, definition, or technique to perform this data-gathering task, and the abundance of different definitions of “depth” and methods for estimating that quantity can lead to misunderstandings in and of the literature. In this review, we describe a wide variety of data sets and methods to analyze those data sets that have been, are currently, or could be used to derive different types of crater depth measurements. We also recommend certain nomenclature in doing so to help standardize practice in the field. We present a review section of all crater depths that have been published on different solar system bodies which shows how the field has evolved through time and how some common assumptions might not be wholly accurate. We conclude with several recommendations for researchers which could help different data sets to be more easily understood and compared.  相似文献   
3.
Impact crater populations help us to understand solar system dynamics, planetary surface histories, and surface modification processes. A single previous effort to standardize how crater data are displayed in graphs, tables, and archives was in a 1978 NASA report by the Crater Analysis Techniques Working Group, published in 1979 in Icarus. The report had a significant lasting effect, but later decades brought major advances in statistical and computer sciences while the crater field has remained fairly stagnant. In this new work, we revisit the fundamental techniques for displaying and analyzing crater population data and demonstrate better statistical methods that can be used. Specifically, we address (1) how crater size-frequency distributions (SFDs) are constructed, (2) how error bars are assigned to SFDs, and (3) how SFDs are fit to power-laws and other models. We show how the new methods yield results similar to those of previous techniques in that the SFDs have familiar shapes but better account for multiple sources of uncertainty. We also recommend graphic, display, and archiving methods that reflect computers’ capabilities and fulfill NASA's current requirements for Data Management Plans.  相似文献   
4.
Constitutive modeling of granular materials has been a subject of extensive research for many years. While the calculation of the Cauchy stress tensor using the discrete element method has been well established in the literature, the formulation and interpretation of the strain tensor are not as well documented. According to Bagi, 1 researchers mostly adopt well‐known continuum or discrete microstructural approaches to calculate strains within granular materials. However, neither of the 2 approaches can fully capture the behavior of granular materials. They are considered complementary to each other where each has its own strengths and limitations in solving granular‐mechanics problems. Zhang and Regueiro 2 proposed an equivalent continuum approach to calculating finite strain measures at the local level in granular materials subjected to large deformations. They used three‐dimensional discrete element method results to compare the proposed strains measures. This paper presents an experimental application of the Zhang and Regueiro 2 approach using three‐dimensional synchrotron microcomputed tomography images of a sheared Ottawa sand specimen. Invariant Eulerian finite strain measures were calculated for representative element volumes within the specimen. The spatial maps of Eulerian octahedral shear and volumetric strain were used to identify zones of intense shearing within the specimen and compared well with maps of incremental particle translation and rotation for the same specimen. The local Eulerian volumetric strain was compared to the global volumetric strains, which also can be considered as an averaging of all local Eulerian volumetric strains.  相似文献   
5.
The Micropile-Mechanically Stabilized Earth (MSE) wall, specially designed for mountain roads, is proposed to improve the MSE wall local stability, global stability and impact resistance of roadside barriers. Model tests and the corresponding numerical modeling were conducted to validate the serviceability of the Micropile-MSE wall and the reliability of the numerical method. Then, a parametric study of the stress and deformation of Micropile-MSE wall based on the backfill strength and interfacial friction angle between backfill and backslope is conducted to evaluate its performance. The test results indicate that the surcharge-induced horizontal earth pressure, base pressure and lateral displacement of the wall panel of Micropile-MSE wall decrease. The corresponding numerical results are nearly equal to the measured values. The basic failure mode of MSE wall in steep terrain is the sliding of backfill along the backslope, while A-frame style micropiles are capable of preventing the sliding trend. The maximum resultant displacement can be decreased by 6.25% to 46.9% based on different interfacial friction angles, and the displacement can be reduced by 6% ~ 56.1% based on different backfill strengths. Furthermore, the reduction increases when the interfacial friction angle and internal friction angle of backfill decrease. In addition, the lateral displacement of wall panel, the deformation of backfill decrease and the tension strain of geogrid obviously, which guarantees the MSE wall functions and provides good conditions for mountain roads.  相似文献   
6.
In the field of offshore oil and gas engineering, the arrangement of multiple pipelines are becoming more common, the spacing between the pipelines and the incoming stream velocity will significantly affect the scouring process around the pipelines. In this study, the effect of space ratio (G/D) and the stream velocity on the scouring process around two pipelines in tandem are investigated using the coupled approach of computational fluid dynamics (CFD) and discrete element method (DEM). Here G is the spacing between the pipelines and D is the diameter of the pipeline. Specifically, the effect of space ratio and the stream velocity are discussed by simulating the gap ratio (G/D) between two pipelines ranging from 1 to 3 with an interval of 1, under the stream velocity U = 0.5,1 and 2 m/s, The results indicate that when G/D ≤ 2, the equilibrium scour depth below the upstream pipeline (S1) is slightly larger than that under the downstream pipeline (S2), S1 and S2 slightly increase as the gap ratio increases. Whereas for G/D > 2, the equilibrium scour depth beneath the upstream pipeline is slightly smaller than that under the downstream pipeline, S1 and S2 slightly decrease as the gap ratio increases. Furthermore, the scour depths are highly dependent on and positively related to the incoming stream velocity, the equilibrium bed profiles are similar under the same incident stream velocity with different gap ratios.  相似文献   
7.
A simplified method with a dynamic Winkler model to study the seismic response of composite caisson–piles foundations (CCPF1) is developed. Firstly, with the dynamic Winkler model, the kinematic response of the CCPF subjected to vertically propagating seismic S-wave is analyzed by coupling the responses of caisson part and pile part. Secondly, a simplified model for the foundation–structure system is created with the structure simplified as a lumped mass connected to the foundation with an elastic column, and through the Fast Fourier Transformation (FFT) this model is enabled to solve transient seismic problems. Thirdly, the proposed method for the seismic response of CCPF-structure systems is verified by comparison against 3D dynamic finite element simulation, in which the Domain Reduction Method (DRM2) is utilized. Lastly, the mechanism and significance of adding piles in improving the earthquake resistance of the foundation and structure is analyzed through an example with different soil conditions. Discovered in this study is that adding piles under the caisson is an efficient way to increase seismic resistant capability of the soil–foundation–structure system, and the main mechanism of that is the elimination of the pseudo-resonance.  相似文献   
8.
9.
In a previous paper (Hou et al. in Celest Mech Dyn Astron 119:119–142, 2014a), the problem of dynamical symmetry between two Jupiter triangular libration points (TLPs) with Saturn’s perturbation in the present configuration of the two planets was studied. A small short-time scale spatial asymmetry exists but gradually disappears with the time going, so the planar stable regions around the two Jupiter TLPs should be dynamically symmetric from a longtime perspective. In this paper, the symmetry problem is studied when the two planets are in migration. Several mechanisms that can cause asymmetries are discussed. Studies show that three important ones are the large short-time scale spatial asymmetry when Jupiter and Saturn are in resonance, the changing orbits of Jupiter and Saturn in the planet migration process, and the chaotic nature of Trojan orbits during the planet migration process. Their joint effects can cause an observable difference to the two Jupiter Trojan swarms. The thermal Yarkovsky effect is also found to be able to cause dynamical differences to the two TLPs, but generally they are too small to be practically observed.  相似文献   
10.
Magnetohydrostatic models of the solar atmosphere are often based on idealized analytic solutions because the underlying equations are too difficult to solve in full generality. Numerical approaches, too, are often limited in scope and have tended to focus on the two-dimensional problem. In this article we develop a numerical method for solving the nonlinear magnetohydrostatic equations in three dimensions. Our method is a fixed-point iteration scheme that extends the method of Grad and Rubin (Proc. 2nd Int. Conf. on Peaceful Uses of Atomic Energy 31, 190, 1958) to include a finite gravity force. We apply the method to a test case to demonstrate the method in general and our implementation in code in particular.  相似文献   
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