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991.
ABSTRACTIn this paper we develop a coupled analytical model for salinity and tidal propagation in estuaries where the cross-sectional area varies exponentially. A simple analytical model for tidal dynamics has been used to estimate the tidal excursion, which has an important influence on the salt intrusion process since it determines the extreme salinities (i.e. salinity distribution for high water slack and low water slack). The objective of the coupling is to reduce the number of calibration parameters, which subsequently strengthens the reliability of the salt intrusion model. Moreover, the coupling enables us to assess the potential impacts of external changes, both human-induced interventions (e.g. dredging) and natural changes (e.g. global sea level rise), on the salt intrusion process. In addition, the fully analytical solution for hydrodynamics allows immediate estimation of the tidally averaged depth and friction coefficient for given water level recordings and salinity measurements. This is particularly useful when a geometric survey is not available. The coupled model has been applied to six previously unsurveyed estuaries in Malaysia and the results show that the correspondence between analytical estimations and observations is very good. Thus, the coupled model proves to be a useful tool to obtain estimates of salt intrusion in estuaries based on a minimum amount of information required and for assessing the effect of human-induced or natural changes.
EDITOR D. Koutsoyiannis ASSOCIATE EDITOR B. Dewals 相似文献
992.
Abstract The singular differential equations for finite temperature relativistic magnetohydrodynamic (MHD) winds integrate to two algebraic equations when the source magnetic field is a monopole. This simplification enables an extensive characterization of the asymptotic wind solutions in terms of source parameters. We will consider only the critical solutions-those that pass smoothly through both an intermediate (Alfvenic) and a fast MHD critical point and expand to zero pressure at infinite radial distance from the source. Because the constants of motion must be specified to extremely high accuracy, the critical solutions cannot be found analytically. Synopsis of many numerical solutions reveals a uniform parametric characterization of the asymptotic wind in terms of one combination of source parameters, Z, the mean source particle energy divided by mc2[sgrave]½, where [sgrave] is a generalization of Michel's (1969) cold relativistic wind strength parameter. Cool winds, with Z<1, behave asymptotically much as Michel's cold wind minimum torque solution; Z1 hot winds have quite different, but simply characterized, asymptotic solutions. Thus, the strength of magnetized relativistic outflows can depend critically upon the temperature of the source. 相似文献
993.
In this study,a new analytical approach is developed to analyze the free nonlinear vibration of conservative two-degree-of-freedom(TDOF) systems.The mathematical models of these systems are governed by second–order nonlinear partial differential equations.Nonlinear differential equations were transferred into a single equation by using some intermediate variables.The single nonlinear differential equations are solved by using the first order of the Hamiltonian approach(HA).Different parameters,which have a significant impact on the response of the systems,are considered and discussed.Some comparisons are presented to verify the results between the Hamiltonian approach and the exact solution.The maximum relative error is less than 2.2124 % for large amplitudes of vibration.It has been established that the first iteration of the Hamiltonian approach achieves very accurate results,does not require any small perturbations,and can be used for a wide range of nonlinear problems. 相似文献
994.
995.
提出了一种加工离轴非球面的预应力环抛方法,基于预应力加工方法的基本原理,利用环抛机来磨制离轴非球面.设计了一套专门的加载装置,将拼接镜面中具有不同离轴量的非球面子镜转化成曲率半径相同的球面子镜进行磨制,可以在同一台环抛机上进行抛光.利用这种方法,花费连续40 h的时间,磨制了一块按照中国30 m极大口径望远镜(CFGT)主镜参数比例缩小的离轴抛物面,顶点曲率半径21.6 m,离轴量3.6 m,离轴口径为330 mm,最大非球面度为16μm.试验表明该方法效率高,适用于批量加工,特别是极大口径天文望远镜拼接主镜的大批量非球面子镜研制. 相似文献
996.
997.
N. KATSUTA I. SHIMIZU H. HELMSTAEDT M. TAKANO S. KAWAKAMI M. KUMAZAWA 《Journal of Metamorphic Geology》2012,30(5):457-472
The Archean (2.8 Ga) Banded Iron Formation (BIF) of the Bell Lake region of Yellowknife greenstone belt, Canada is recrystallized to metamorphic assemblages of the amphibolite facies. This BIF is characterized by centimetre‐scale Fe‐rich and Si‐rich mesobands. In the Si‐rich mesobands, thin layers of magnetite microbands are developed in a quartz matrix. The Fe‐rich mesobands are composed mainly of Ca‐amphibole (hornblende), Fe–Mg amphibole (grunerite), and magnetite. The metamorphic foliation locally cuts across the mesoband boundaries, indicating the mesobanding was formed prior to peak metamorphism. Variations in mineral modal proportions between Fe‐rich mesobands and microbands are diagnostic of depositional compositional differences between beds. Micro‐X‐ray fluorescence imaging reveals metamorphic differentiation within Fe‐rich mesobands, with segregation of Fe–Mg amphibole, and the incompatible element Mn is concentrated at the margins of the Fe‐rich mesobands during the amphibole‐forming reactions. Ti was relatively immobile during metamorphic segregation and its distribution provides a record of the original structures in the Fe‐rich mesobands. 相似文献
998.
Existing solutions for analyzing one-dimensional (1-D) consolidation of unsaturated soil are only derived to cater to two extreme drainage conditions (fully drained and undrained). This study presents a new explicit solution for 1-D consolidation of unsaturated soil with semi-permeable drainage boundary. Based on the assumptions of two independent stress variables and the governing equations proposed by Fredlund, the eigenfunction expansion method is adopted to develop an explicit analytical solution to calculate excess pore-water and pore-air pressures in an unsaturated soil when it is subjected to external loads. The developed general solutions are expressed in terms of depth, z, and time, t. For the semi-permeable drainage boundary, eigenvalues and eigenfunctions in the space domain are developed. The technique of Laplace transform is used to solve the coupled ordinary differential equations in the time domain. The newly derived explicit solution is verified with the existing semi-analytical method in the literature, and an excellent agreement is obtained. Compared with the semi-analytical solution, the newly derived analytical solution is more straightforward and explicit so that this solution is relatively easier to be implemented into a computer program to carry out a preliminary assessment of 1-D consolidation of unsaturated soil. 相似文献
999.
A thermomechanical anisotropic continuum model for geological materials with multiple joint sets 
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下载免费PDF全文 Joints in geological materials introduce elastic compliance and weak planes on which sliding can occur. Although these materials can have multiple joint sets, they often have preferred orientations that cause both elastic and inelastic anisotropic response even when the unjointed material is isotropic. Azimuthal variations in radial velocity and polarity of tangential motion have been observed in experimental data for wave propagation caused by an initially spherical source in a geological material with multiple joint sets. This observed tangential ground motion was found to be related to mechanical anisotropy caused by preferred orientations of joints in the rock. This paper describes thermomechanical continuum constitutive equations, which model the effects of multiple persistent joint sets. A number of quasi‐static examples are considered, which show that the proposed model predicts anisotropic effects of sliding on multiple joint sets similar to those exhibited by computationally expensive mesoscale calculations, which model joint sets explicitly. 相似文献
1000.
An approximate static solution is derived for the elastic settlement and load-transfer mechanism in axially loaded end-bearing piles in inhomogeneous soil obeying a power law variation in shear modulus with depth. The proposed generalised formulation can handle different types of soil inhomogeneity by employing pertinent eigenexpansions of the dependent variables over the vertical coordinate, in the form of static soil “modes”, analogous to those used in structural dynamics. Contrary to available models for homogeneous soil, the associated Fourier coefficients are coupled, obtained as solutions to a set of simultaneous algebraic equations of equal rank to the number of modes considered. Closed-form solutions are derived for the (1) pile head stiffness; (2) pile settlement, axial stress, and side friction profiles leading to actual, depth-dependent Winkler moduli, (3) displacement and stress fields in the soil; and (4) average, depth-independent Winkler moduli to match pile head settlement. The predictive power of the model is verified via comparisons against finite element analyses. The applicability to inhomogeneous soil of an existing regression formula for the average Winkler modulus is explored. 相似文献