黄河壶口瀑布国家地质公园开发建设构想

地质公园是地质遗迹景观和生态环境的重点保护区,是地质科学研究与普及的基地。黄河壶口瀑布的形成经历了一个复杂而漫长的演化过程。显露在河床及河谷两岸的地质遗迹,揭示着黄河壶口瀑布演化进程,对研究黄河发育史、晋陕峡谷的形成、瀑布成因、演化等问题,具有重要的科学理论价值。因此对黄河壶口瀑布国家地质公园的地质旅游资源进行了科学的综合评价,提出了开发构想。使黄河壶口瀑布地质地貌能得以科学的保护与合理的开发利用,不仅要将壶口瀑布建成我国著名的地质公园,更要将其建成我国的瀑布科学研究中心和科普教育基地。     

Evaluating Models Of The Neutral, Barotropic Planetary Boundary Layer Using Integral Measures: Part Ii. Modelling Observed Conditions

The steady-state, horizontally homogeneous, neutral, barotropiccase forms the foundation of our theoretical understanding of the planetary boundary layer (PBL).While simple analytical models and first-order closure models simulate atmospheric observationsof this case well, more sophisticated models, in general, do not. In this paperwe examine how well three higher-order closure models, E - - l, E - l, and LRR - l,which have been especially modified for PBL applications, perform in predicting the behaviour of thecross-isobaric angle ₀, the geostrophic drag coefficient C_g, and the integral of the dissipationrate over the boundary layer, as a function of the surface Rossby number Ro. For comparison we alsoexamine the performance of three first-order closure mixing-length models, two proposed byA. K. Blackadar and one by H. H. Lettau, and the performance of the standard model forsecond-order closure and a modification of it designed to reduce the overprediction of turbulence inthe upper part of the boundary layer.     

Estimation of dynamic ocean topography in the Gulf Stream area using the Hotine formula and altimetry data

Two modifications of the Hotine formula using the truncation theory and marine gravity disturbances with altimetry data are developed and used to compute a marine gravimetric geoid in the Gulf Stream area. The purpose of the geoid computation from marine gravity information is to derive the absolute dynamic ocean topography based on the best estimate of the mean surface height from recent altimetry missions such as Geosat, ERS-1, and Topex. This paper also tries to overcome difficulties of using Fast Fourier Transformation (FFT) techniques to the geoid computation when the Hotine kernel is modified according to the truncation theory. The derived absolute dynamic ocean topography is compared with that from global circulation models such as POCM4B and POP96. The RMS difference between altimetry-derived and global circulation model dynamic ocean topography is at the level of 25cm. The corresponding mean difference for POCM4B and POP96 is only a few centimeters. This study also shows that the POP96 model is in slightly better agreement with the results derived from the Hotine formula and altimetry data than POCM4B in the Gulf Stream area. In addition, Hotine formula with modification (II) gives the better agreement with the results from the two global circulation models than the other techniques discussed in this paper. Received: 10 October 1996 / Accepted: 16 January 1998     

A comparison of drainage networks derived from digital elevation models at two scales

Automated generation of drainage networks has become increasingly popular with powerful analytical functions in geographic information systems (GIS) and with the increased availability of digital elevation models (DEMs). This paper compares drainage networks derived from DEMs at two scales, 1:250 000 (250K) and 1:24 000 (24K), using various drainage parameters common in hydrology and geomorphology. The comparison of parameters derived from the 250K DEMs with those from the 24K DEMs in 20 basins ranging from 150 to 1000 km² in West Virginia shows that the goodness-of-fit between parameter estimates based on the DEMs varies. Results clearly show that superior estimations are produced from the 24K DEMs. Better estimates can be obtained from the 250K DEMs for stream length and frequency parameters than for gradient parameters. However, the estimation of the mean gradient parameters based on the 250K DEMs seems to improve with increasing terrain complexity. Finally, basin size does not strongly affect the accuracy of parameter estimates based on the 250K DEMs.     

Statistical estimation of corner frequency and its application to seismic event-identification

A statistical method is proposed for estimation of the corner frequency. It is based on inference for a stochastic model whose short-term behavior resembles the established source time functions. Properties of the estimates are investigated and some numerical examples are presented. A discussion concerning earthquake–explosion discrimination and the way corner frequency can be related to the rate of zero-crossings is also included. The paper is concluded with some numerical examples.     

Computer-simulation models of scoria cone degradation

Long-term erosional modifications of the relatively simple morphology of scoria (‘cinder') cones are ideally suited for study by field and computer-simulation methods. A series of temporally-distinct cones in the San Francisco and Springerville volcanic fields of Arizona provides the foundation for documenting the degradational evolution of scoria cones in a semi-arid climate. Progressive changes due to erosion are illustrated by the systematic decrease with increasing age of various morphometric parameters, including scoria cone height, cone height/width ratio (H_co/W_co), crater depth/width ratio, and slope angle. For example, Holocene–latest Pleistocene cones in the San Francisco field have a mean H_co/W_co value of 0.178±0.041, a mean maximum slope angle of 29.7±4.2°, and a mean average slope angle of 26.4±7.3°, whereas the group of Pliocene cones have values of 0.077±0.024, 20.5±5.8°, and 8.7±2.7°, respectively. Comparative morphology of scoria cones is a potentially useful dating tool for mapping volcanic fields.In order to better understand the degradational modifications of these volcanic landforms, we have developed a numerical approach to simulate the surficial processes responsible for the erosion of a typical scoria cone. The simulation algorithm can apply either a linear diffusion-equation model or a model with a nonlinear transport law. Using a finite-difference formulation, the simulation operates upon a three-dimensional scoria cone input as a matrix of elevation values. Utilizing both field and model results, the correlation between changing H_co/W_co value, cone age, and computer time step was expressed graphically to derive comprehensive values of the transport or diffusion coefficient (D_f) for both volcanic fields. For the San Francisco volcanic field, D_f had a calculated value of 21.4 m²/kyr for the linear model and 5.3 m/kyr for the nonlinear model, while for the Springerville volcanic field D_f had a calculated value of 24.4 m²/kyr for the linear model and 6.3 m/kyr for the nonlinear model.     

Formulation of discontinuous deformation analysis (DDA) — an implicit discrete element model for block systems

Continuum-based numerical methods have played a leading role in the numerical solution of problems in rock mechanics and engineering geology. However, for fractured rocks, a continuum assumption often leads to difficult parameters to define and over-simplified geometry to be realistic. In such case, discrete representations of fractures and individual blocks must be adopted. In this paper, a newly emerged member in the family of discrete element methods (DEM), the discontinuous deformation analysis (DDA), is presented, including its variational principle, governing equations, solution techniques and contact representation and detection algorithms. Its relative advantages and shortcomings are compared with the explicit distinct element method and the finite element method. An example of the analysis of tunnel stability is provided to demonstrate the capability of this new method.     

应用CARMA模型评价矿井疏水对泉流量的影响

受控自回归滑动平均模型是用来描述随机现象中输入与输出关系的一类线性动态模型。本文以大柳塔井田双沟泉域为例,应用该模型分别对双沟泉域在天然条件和矿井疏水条件下的泉流量进行预测,并据此评价矿井疏水对泉流量的影响。     

川东地区天然气勘探开发的三种模式

本文根据川东地区天然气勘探开发历史,系统归纳和总结了成组气田整体勘探开发、多高点滚动勘探开发和多产层立体勘探开发三种模式的勘探程序、勘探部署以及开发特点和原则。以供后续天然气勘探开发决策时参考。     

盾构隧道衬砌结构受力分析的梁—弹簧系统模型

盾构隧道衬砌结构由若干管片及其间的连接螺栓组成。在其断面受力的工程设计中,目前普遍采用梁-弹簧系统模型来模拟其受力性态。其中,梁可分成直梁和曲梁两类。本文在考虑弹簧刚度的轴向、切向和转动效应的同时,从卡氏（Castigliano）第二定理出发,给出了梁-弹簧模型的矩阵式,并论证了直梁-弹簧模型与曲梁-弹簧模型的一致性关系。在数值模拟计算过程中,还考虑了地层反作用力非线性情形和管片接头转动刚度正、负弯矩时的非对称性问题。