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101.
The magnetic method is the oldest and one of the most widely used geophysical techniques for exploring the earth’s subsurface.
It is a relatively easy and inexpensive tool to employ, being applicable to a wide variety of subsurface exploration problems
involving horizontal magnetic property variations occurring from near the base of the crust to within the uppermost meter
of soil. Successful applications of the magnetic method require an in-depth understanding of its basic principles and careful
field work, data reduction, and interpretation. Commonly, interpretations are limited to qualitative approaches which simply
map the spatial location of anomalous subsurface conditions, but under favourable circumstances the technological status of
the method will permit more quantitative interpretations involving specification of the nature of the anomalous sources. No
other geophysical method provides critical input to such a wide variety of problems. However, seldom does the magnetic method
provide the complete answer to an investigation problem. As a result, it is generally used in concert with other geophysical
and geological data to limit its interpretational ambiguities. 相似文献
102.
Latent spatio-temporal activity structures: a new approach to inferring intra-urban functional regions via social media check-in data 总被引:1,自引:0,他引:1
AbstractThis article introduces a novel low rank approximation (LRA)-based model to detect the functional regions with the data from about 15 million social media check-in records during a year-long period in Shanghai, China. We identified a series of latent structures, named latent spatio-temporal activity structures. While interpreting these structures, we can obtain a series of underlying associations between the spatial and temporal activity patterns. Moreover, we can not only reproduce the observed data with a lower dimensional representative, but also project spatio-temporal activity patterns in the same coordinate system. With the K-means clustering algorithm, five significant types of clusters that are directly annotated with a combination of temporal activities can be obtained, providing a clear picture of the correlation between the groups of regions and different activities at different times during a day. Besides the commercial and transportation dominant areas, we also detected two kinds of residential areas, the developed residential areas and the developing residential areas. We further interpret the spatial distribution of these clusters using urban form analytics. The results are highly consistent with the government planning in the same periods, indicating that our model is applicable to infer the functional regions from social media check-in data and can benefit a wide range of fields, such as urban planning, public services, and location-based recommender systems. 相似文献
103.
AbstractDeep-sea mining (DSM) is an advanced technology. This article is focused on the dynamic analysis of a coupled vessel/riser/equipment system of a DSM based on radial basis function (RBF) neural network approximations while considering vessel dynamic positioning (DP) and active heave compensation (AHC). A coupled model including the production support vessel (PSV), lifting riser, and slurry pump is established containing simulated DP and AHC models. Furthermore, dynamic simulations are implemented to obtain the results of the vessel motions, thruster forces, pump motions and riser tensions. Using optimal Latin hypercube sampling, an RBF neural network approximation model is established, the input includes environmental factors and the output includes the dynamic responses of the pump motion and riser tension. Calculations are performed using RBF network approximations instead of a coupled model. The obtained results show that the PSV wave frequency (WF) motions have significant influence on the dynamic responses of the subsea system. Moreover, the current load affects the compensation effect. The RBF network approximation model can be used to reduce the required calculation time. 相似文献
104.
A new set of Boussinesq-type equations describing the free surface evolution and the corresponding depth-integrated horizontal velocity is derived with the bottom boundary layer effects included. Inside the boundary layer the eddy viscosity gradient model is employed to characterize Reynolds stresses and the eddy viscosity is further approximated as a linear function of the distance measured from the seafloor. Boundary-layer velocities are coupled with the irrotational velocity in the core region through boundary conditions. The leading order boundary layer effects on wave propagation appear in the depth-integrated continuity equation to account for the velocity deficit inside the boundary layer. This formulation is different from the conventional approach in which a bottom stress term is inserted in the momentum equation. An iterative scheme is developed to solve the new model equations for the free surface elevation, depth-integrated velocity, the bottom stress, the boundary layer thickness and the magnitude of the turbulent eddy viscosity. A numerical example for the evolution of periodic waves propagating in one-dimensional channel is discussed to illustrate the numerical procedure and physics involved. The differences between the conventional approach and the present formulation are discussed in terms of the bottom frictional stress and the free surface profiles. 相似文献
105.
刘新国 《中国海洋大学学报(自然科学版)》1996,(3)
研究两个线性最小二乘问题解流形之间的逼近性。所得结果可看作普通最小二乘问题扰动理论的继续。推广了若干已有结论。 相似文献
106.
Zhang Yonggang Li Yucheng Teng Bin
Doctor Degree Candidate The National Key Laboratory of Coastal Offshore Engineering Dalian University of Technology Dalian
Professor The National Key Laboratory of Coastal Offshore Engineering Dalian University of Technology Dalian
Associate Professor The National Key Laboratory of Coastal Offshore Engineering Dalian University of Technology Dalian 《中国海洋工程》1995,(4)
The mild-slope equation derived by Berkhoff (1972), has widely been used in the numerical calculation of refraction and diffraction of regular waves. However, it is well known that the random sea waves has a significant effect in the refraction and diffraction problems. In this paper, a new form of time-dependent mild slope equation for irregular waves was derived with Fade approximation and Kubo's time series concept. The equation was simplified using WKB method, and simple and practical irregular mild slope equation was obtained. Results of numerical calculations are compared with those of laboratory experiments. 相似文献
107.
With the horizontal Coriolis terms included in motion equations and the influence of compressibility of seawater on Brunt-Visl frequency considered, a numerical method of calculating the dispersion relation for linear internal waves, which is an improvement of Cai and Gan (1995), and hence Fliegel and Hunkins (1975), had been set up. For different models (Pacific model, Atlantic model and Arctic model), simulations using the three different methods were compared and the following conclusions were reached:(1) the influence of horizontal Coriolis terms on dispersion relation cannot be neglected and is connected with the direction of the wave celerity, the latitude, and the modes of the wave;(2) the effect of compressibility of seawater in stratification is not an important factor for the dispersion relation of linear internal wave, at least for those three models. With the improved method, the wavefunction curves for the Pacific model had also been built. 相似文献
108.
GNSS动态相对定位中常附加非线性的基线长约束进行解算, 而LAMBDA方法只能处理无约束或者线性约束的模型, 为了应用LAMBDA方法, 应对非线性约束条件进行线性化近似。通常附加该约束后, 模糊度固定成功率会提高, 但对于超短基线有时反而会降低。何种条件下附加线性化近似的基线长约束条件可以提高模糊度固定成功率尚未有定论。本文基于附加基线长约束的GNSS相对定位数学模型, 推导基线长约束条件线性化近似余项对浮点解的最大影响值公式, 给出基线长约束能否线性化近似的诊断条件。当该条件满足时, 线性化近似余项影响可以忽略, 附加线性化近似的基线长约束可以改善浮点解解算精度, 提高模糊度固定成功率;若不满足, 则线性化近似余项影响可能不可以忽略, 附加约束会因浮点解有偏不能固定为正确的模糊度, 并通过算例验证了相关结论。 相似文献
109.
110.
Although rainfall is assumed spatially uniform in conventional hydrological modelling for rainfall–runoff simulations, moving storms have been shown to have substantial influence on flow hydrographs. In this study, criteria for attainment of the equilibrium discharge from watersheds subjected to moving storms were examined. Non-linear numerical kinematic-wave models were developed to simulate runoff from an overland plane and from a V-shaped catchment. Dimensional analysis was applied to obtain the independent variables to be used as control factors in performing a series of numerical tests. The results indicate that, for storms moving downstream, runoff can attain equilibrium discharge even though the storm length is shorter than the watershed length and the rainfall duration is less than the time to equilibrium of the watershed for stationary uniform storms. The phenomenon of attainment of equilibrium discharge from watersheds subjected to moving storms is contradictory to conventional hydrologic design, which assumes the storm duration must equal the time to equilibrium to attain the maximum discharge. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献