基于多项式拟合均匀荷载面曲率曲线的结构损伤识别方法

为仅利用结构损伤状态的柔度矩阵对结构进行损伤程度识别,先对损伤状态的均匀荷载面曲率曲线进行最小二乘法拟合。根据曲率曲线差判断结构的损伤位置,对损伤位置的点进行剔除后,再利用未损伤位置上的点进行局部最小二乘法拟合,代替损伤前的均匀荷载面曲率曲线,用于结构的损伤定位与定量。通过一简支梁数值算例,先以理论的二次多项式进行拟合,考虑单损伤和多损伤的情况,进行损伤识别分析,再分析多项式次数、测点数目以及不同噪声水平对损伤定量精度的影响。结果表明:在一定范围内,次数越高拟合误差越小,但差别不明显,采用理论的二次多项式拟合即可满足结构损伤识别要求,无噪声的情况下,测点数目减半不影响损伤识别的精度,该方法具有一定的抗噪声能力。     

Determination of the drainage structure of a watershed using a digital elevation model and a digital river and lake network

Distributed hydrological models require a detailed definition of a watershed's internal drainage structure. The conventional approach to obtain this drainage structure is to use an eight flow direction matrix (D8) which is derived from a raster digital elevation model (DEM). However, this approach leads to a rather coarse drainage structure when monitoring or gauging stations need to be accurately located within a watershed. This is largely due to limitations of the D8 approach and the lack of information over flat areas and pits. The D8 approach alone is also unable to differentiate lakes from plain areas.

To avoid these problems a new approach, using a digital river and lake network (DRLN) as input in addition to the DEM, has been developed. This new approach allows for an accurate fit between the DRLN and the modelled drainage structure, which is represented by a flow direction matrix and a modelled watercourse network. More importantly, the identification of lakes within the modelled network is now possible. The proposed approach, which is largely rooted in the D8 approach, uses the DRLN to correct modelled flow directions and network calculations. For DEM cells overlapped by the DRLN, flow directions are determined using DRLN connections only. The flow directions of the other DEM cells are evaluated with the D8 approach which uses a DEM that has been modified as a function of distance to the DRLN.

The proposed approach has been tested on the Chaudière River watershed in southern Québec, Canada. The modelled watershed drainage structure showed a high level of coherence with the DRLN. A comparison between the results obtained with the D8 approach and those obtained by the proposed approach clearly demonstrated an improvement over the conventionally modelled drainage structure. The proposed approach will benefit hydrological models which require data such as a flow direction matrix, a river and lake network and sub-watersheds for drainage structure information.     

Gravitational attraction and potential of spherical shell with radially dependent density

Solutions to the direct problem in gravimetric interpretation are well-known for wide class of source bodies with constant density contrast. On the other hand, sources with non-uniform density can lead to relatively complicated formalisms. This is probably why analytical solutions for this type of sources are rather rare although utilization of these bodies can sometimes be very effective in gravity modeling. I demonstrate an analytical solution to that problem for a spherical shell with radial polynomial density distribution, and illustrate this result when applied to a special case of 5th degree polynomial. As a practical example, attraction of the normal atmosphere is calculated.     

Thresholds of geographic environmental elements in sediment yield of drainage basins

Threshold of environmental elements in drainage basin sediment yield refers to, under effect of climate, underlying surface and human activity, a turning point of abrupt changes in drainage sediment yield related to environmental element characteristics. Previous studies on threshold of sediment yield of relevant drainage basins were mainly concentrated on impact of natural zones with a few researches on impact of other environmental elements. Particularly studies on compound environmental element threshold in drainage basin sediment yield remain blank today. Studies indicate that sediment yield in drainage basins is affected by compound interactions and complex actions. Based on single element analysis, the present paper gives quantitatively compound threshold of environmental elements affecting sediment yield of the drainage basin between Hekouzhen and Tongguan in the middle Yellow River by the method of multi-variant, polynomial formula regression analysis.     

压制多次波的正交多项式谱减法

本文提出了一种新的压制多次波的正交多项式谱减法.将地震资料经过正交多项式变换,其高阶系数谱主要体现了多次波特征.根据多次波低阶系数谱与高阶系数谱之间的关系,估计出多次波的低阶系数谱,从地震记录正交多项式系数谱中减去多次波的系数谱得到一次波的正交多项式系数谱.该方法较好地解决了一次波和多次波在正交多项式谱混叠的问题,尤其在近偏移距有效地分离了多次波和一次波,同时能够较好地保护地震信号中的AVO(amplitude versus offset,振幅随偏移距变化)信息.人工合成数据处理结果表明了所提出方法的有效性.     

Analysis of a reconnaissance gravity survey for drift-filled valleys in the Mercer quadrangle, Pennsylvania

The effectiveness of a standard polynomial trend removal technique and two-dimensional wavenumber filtering in isolating gravity anomalies due to buried preglacial drainage systems was evaluated for an area in northwestern Pennsylvania. It was found that gravity surveying is a useful reconnaissance technique in this area. Both analytical methods isolated anomalies due to valleys of major hydrological interest, provided similar useful information on the valley trends, and gave reasonably accurate width estimates. Accurate depth estimates could not be inferred, although large anomalies generally coincided with thicker drift accumulations. With the station spacing used (about 0.75 miles), valleys sought must have drift accumulations in excess of 75 feet and widths of at least one mile if they are to be adequately resolved. The two-dimensional filtering method seems to offer the most complete information, while still being practical, and it avoids many of the problems of the polynomial method.     

OPTIMAL POLYNOMIAL CONTROL FOR SEISMICALLY EXCITED NON-LINEAR AND HYSTERETIC STRUCTURES

In this paper, we present an optimal polynomial controller for reducing the peak response quantities of seismically excited non-linear or hysteretic building systems. A performance index, that is quadratic in control and polynomial of any order in non-linear states, is considered. The performance index is minimized based on the Hamilton–Jacobi–Bellman equation using a polynomial function of non-linear states, which satisfies all the properties of a Lyapunov function. The resulting optimal controller is a summation of polynomials in non-linear states, i.e. linear, cubic, quintic, etc. Gain matrices for different parts of the controller are determined from Riccati and Lyapunov matrix equations. Numerical simulation results indicate that the percentage of reduction for the selected peak response quantity increases with the increase of the earthquake intensity. Such load adaptive properties are very desirable, since the intensity of the earthquake ground acceleration is stochastic in nature. The proposed optimal polynomial controller is an effective and viable control method for non-linear or hysteretic civil engineering structures. It is an addition to available control methods in the literature.     

位移观测值协方差矩阵模拟及其在整体解算地壳应变场中的应用

借助高斯型函数模拟分散分布的不同监测网点位移观测值的协方差矩阵,并将其应用于广东新丰江地区地壳应变场的计算中．结果表明：本文的方法不仅计算简便,模拟效果及计算稳定性较好,而且对联系分散分布的单元有一定的意义     

THE VARIATION OF DRAINAGE DENSITY WITHIN A CATCHMENT

Abstract

Actual discharges from two experimental catchments are related to the corresponding measurements of the length of channel flow; within a single catchment this is equivalent to drainage density. Drainage densities ranging from less than 1.0 to nearly 10.0 are associated with discharges ranging from 0.15 to nearly 20.0 c.f.s. per square mile. In each catchment all discharge values (Q) and drainage density values (Dd) are related by a function approximately of the form Q ∝ Dd², which is then discussed in relation to studies made of the variation of streamflow and drainage density between catchments. It is suggested that both peak flow and base flow are related to drainage density in the same way. Studies which include drainage density as a basin characteristic and which relate it to water yield should acknowledge that its value varies within any one catchment, and therefore that the drainage density values derived by a particular method can be related only to one type of flow. In Great Britain the watercourses shown on the 1:10,560 maps relate to specific low flow discharges.     

Conflicting drainage patterns in the Matera Horst Area,southern Italy

The Matera Horst (“Murgia materana”) is included in the Apulian plateau, basically formed by Mesozoic shallow-water carbonates. The zone is located in a present-day temperate belt and form a flat-topped morphostructural large element inside the foreland area of the southern Apennines. This horst is bordered by high-angle faults and surrounded by downthrown blocks covered by Plio-Quaternary marine and alluvial sediments. The structural high experienced several morphological cycles from Miocene to Quaternary. In particular, three evolutionary stages can be recognized at least. The first stage is currently represented by relics of a flat erosional landscape at the top of the relieves. The second one is testified by gentle slopes with wide glacis at the foothills, locally covered by coarse waste deposits. During the third stage a series of marine terraces formed and a drainage system developed creating both bland valleys and well-defined channels and gorges. The latter streams deeply carve the Cretaceous limestone of the Matera Horst for they represent the morphological response to the tectonic uplift of the area and clearly post-date the former features. Since the fluvial net took place on Pleistocene covers, later widely eroded, it is possible to conclude that the major part of the Matera Horst drainage system represents a good example of superimposition. However, low order streams and segments of major rivers appear to be structurally controlled, as suggested by comparison with the fracture system. Further, also open synclines and gently steeped flexures may locally exert a driving control on minor streams. These apparently conflicting genetic hypotheses can be explained by the role of exhumation of inherited structures of the bedrock in add to a constant interplay between tectonics, erosion and drainage evolution during Quaternary times.     

ESTIMATION OF THE DEGREE OF POLYNOMIAL FITTED TO GRAVITY ANOMALIES AND ITS APPLICATION1

A method for estimating the degree of polynomial fitted to gravity anomalies to evaluate the regional anomaly is presented. The anomaly can be fitted by polynomials of different degrees with the least-squares method and the optimum degree of the polynomial evaluating this anomaly can be estimated from the point of discontinuity of the gradient on a graph of variance against the polynomial degree. The Bouguer gravity is initially separated by upward continuation to a proper height and then the degree of regional polynomial to fit the Bouguer anomaly can be estimated. Theoretical and field examples show the effectiveness of the method.     

Run‐off formation in a humid,temperate headwater catchment using a combined hydrological,hydrochemical and isotopic approach (Jizera Mountains,Czech Republic)

The formation of baseflow and stormflow was examined in the 1.18 km² part of the headwater catchment Uhlí?ská, Jizera Mountains, Czech Republic, over the period 2007–2011, by means of run‐off data and environmental tracers ¹⁸O and SiO₂. The baseflow, computed using the digital filter approach BFLOW, contributes 67% to total streamflow and has a mean residence time of 12.3 months. It is formed by groundwater discharge from the valley deluviofluvial granitic sediments, in combination with soil water in weathered layers on hillslopes during rainfall and snowmelt periods. The prevailing source of the groundwater is the infiltration of snowmelt water. Analysis of 20 run‐off events and their hysteretic patterns demonstrated that the stormflow water has a residence time of about 4 months and is generated by preferential flow on hillslopes combined by soil matrix drainage. Because of slower flow in the soil matrix, the enrichment of pore water in SiO₂ is more pronounced. The stormflow and snowmelt water flowing via preferential pathways of upslope minerals soils pushes the pre‐event groundwater through the pathways in wetlands to the stream, and the wetland can be therefore considered as groundwater supplied. This mechanism has been found to be typical for the groundwater‐supplied headwater catchments of the Jizera Mountains and can be also assumed in other mountainous headwaters of the granitic massif in Central Europe. The main methodological contribution of this study are the residence time calculations stratified by baseflow and event flow, identifying run‐off components of different travel times to streams and linking them with geochemical run‐off sources. This achievement was possible because of a comprehensive dataset on hydrology, stable isotopes and silica hydrochemistry in all relevant run‐off generation components. This concept indicates that a possible long‐term change in snowmelt may affect the run‐off regime of headwater catchments to climate or land‐use changes. Copyright © 2013 John Wiley & Sons, Ltd.     

Quantitative analysis of land surface topography

Land surface topography significantly affects the processes of runoff and erosion. A system which determines slope, aspect, and curvature in both the down-slope and across-slope directions is developed for an altitude matrix. Also, the upslope drainage area and maximum drainage distance are determined for every point within the altitude matrix. A FORTRAN 66 program performs the analysis.     

The future danger of Mt. Kelut (Eastern Java — Indonesia)

The tunnel system of Hettinga Tromp proved that the Kelut dangers can be controlled to such an extend that no great lahars were formed during the eruption of 1951. This eruption, however, destroyed these tunnels. In 1954, a drainage tunnel system was built based on the seepage principle. But till now it has failed to drain the lake completely. The 23.5 million cb.m of water still stored up in its crater lake will form a potential danger during an eventual eruption.     

An iterative scheme for use in MT 2D forward modelling — to speed up production of the Jacobian and to improve accuracy of the inverse matrix

An important stage in two-dimensional magnetotelluric modelling is the calculation of the Earth's response functions for an assumed conductivity model and the calculation of the associated Jacobian relating those response functions to the model parameters. The efficiency of the calculation of the Jacobian will affect the efficiency of the inversion modelling. Rodi (1976) produced all the Jacobian elements by inverting a single matrix and using an approximate first-order algorithm. Since only one inverse matrix required calculation the procedure speeded up the inversion. An iterative scheme to improve the approximation to the Jacobian information is presented in this paper. While this scheme takes a little longer than Rodi's algorithm, it enables a more accurate determination of the Jacobian information. It is found that the Jacobian elements can be produced in 10% of the time required to calculate an inverse matrix or to calculate a 2D starting model. A modification of the algorithm can further be used to improve the accuracy of the original inverse matrix calculated in a 2D finite difference program and hence the solution this program produces. The convergence of the iteration scheme is found to be related both to the originally calculated inverse matrix and to the change in the newly formed matrix arising from perturbation of the model parameter. A ridge regression inverse algorithm is used in conjunction with the iterative scheme for forward modelling described in this paper to produce a 2D conductivity section from field data.     

INVERSION OF GRAVITY PROFILES BY POLYNOMIAL METHOD *

The inversion of a gravity profile associated with a twodimensional distribution of mass with constant difference in density is dealt with, in an initial approximation, by using a polynomial of appropriate degree. The method can be applied successfully, for example, to sedimentary basins. Some examples confirm the applicability of the method, which can be readily programmed on a computer.     

From rainfall to spring discharge: Coupling conduit flow,subsurface matrix flow and surface flow in karst systems using a discrete–continuum model

Physics-based distributed models for simulating flow in karst systems are generally based on the discrete–continuum approach in which the flow in the three-dimensional fractured limestone matrix continuum is coupled with the flow in discrete one-dimensional conduits. In this study we present a newly designed discrete–continuum model for simulating flow in karst systems. We use a flexible spatial discretization such that complicated conduit networks can be incorporated. Turbulent conduit flow and turbulent surface flow are described by the diffusion wave equation whereas laminar variably saturated flow in the matrix is described by the Richards equation. Transients between free-surface and pressurized conduit flow are handled by changing the capacity term of the conduit flow equation. This new approach has the advantage that the transients in mixed conduit flow regimes can be handled without the Preissmann slot approach. Conduit–matrix coupling is based on the Peaceman’s well-index such that simulated exchange fluxes across the conduit–matrix interface are less sensitive to the spatial discretization. Coupling with the surface flow domain is based on numerical techniques commonly used in surface–subsurface models and storm water drainage models. Robust algorithms are used to simulate the non-linear flow processes in a coupled fashion. The model is verified and illustrated with simulation examples.     

Precise arrival time detection of polarized seismic waves using the spectral matrix

I present a statistical method for detecting the arrival times of polarized seismic waves on three-component seismic observations in the time and frequency domains. In this method, the polarization, which is a representation of the 3D particle motion of seismic waves, is evaluated on the basis of a spectral matrix in the time and frequency domains and the statistical parameters are defined by using the eigenvalues of the spectral matrix for detecting the arrival times of linearly and elliptically polarized waves, where the idea of a statistical test of hypothesis is introduced. An evaluation of a synthetic signal revealed that the method can detect the arrival times of linearly and elliptically polarized waves within 10 sampling points at signal-to-noise ratios of −7 dB. Application of the method to an earthquake suggested that it can be used to detect the arrival times of both linearly and elliptically polarized waves, which are difficult to identify manually.     

Iterative implicit integration procedure for hybrid simulation of large nonlinear structures

A fully implicit iterative integration procedure is presented for local and geographically distributed hybrid simulation of the seismic response of complex structural systems with distributed nonlinear behavior. The purpose of this procedure is to seamlessly incorporate experimental elements in simulations using existing fully implicit integration algorithms designed for pure numerical simulations. The difficulties of implementing implicit integrators in a hybrid simulation are addressed at the element level by introducing a safe iteration strategy and using an efficient procedure for online estimation of the experimental tangent stiffness matrix. In order to avoid physical application of iterative displacements, the required experimental restoring force at each iteration is estimated from polynomial curve fitting of recent experimental measurements. The experimental tangent stiffness matrix is estimated by using readily available experimental measurements and by a classical diagonalization approach that reduces the number of unknowns in the matrix. Numerical and hybrid simulations are used to demonstrate that the proposed procedure provides an efficient method for implementation of fully implicit numerical integration in hybrid simulations of complex nonlinear structures. The hybrid simulations presented include distributed nonlinear behavior in both the numerical and experimental substructures. Copyright © 2010 John Wiley & Sons, Ltd.     

TSVD analysis of Euler deconvolution to improve estimating magnetic source parameters: An example from the Åsele area,Sweden

In this paper, I introduce a new approach based on truncated singular value decomposition (TSVD) analysis for improving implementation of grid-based Euler deconvolution with constraints of quasi 2D magnetic sources. I will show that by using TSVD analysis of the gradient matrix of magnetic field anomaly (reduced to pole) for data points located within a square window centered at the maximum of the analytic signal amplitude, we are able to estimate the strike direction and dip angle of 2D structures from the acquired eigenvectors. It is also shown that implementation of the standard grid-based Euler deconvolution can be considerably improved by solving the Euler's homogeneity equation for source location and structural index, simultaneously, using the TSVD method. The dimensionality of the magnetic anomalies can be indicated from the ratio between the smallest and intermediate eigenvalues acquired from the TSVD analysis of the gradient matrix. For 2D magnetic sources, the uncertainty of the estimated source location and structural index is significantly reduced by truncating the smallest eigenvalue.Application of the method is demonstrated on an aeromagnetic data set from the Åsele area in Sweden. The geology of this area is dominated by several dike swarms. For these dolerite dikes, the introduced method has provided useful information of strike directions and dip angles in addition to the estimated source location and structural index.