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1.
JiangWenbo HeZhanxiang LiuHong 《应用地球物理》2003,6(1):22-26
Addressed in this article is a new approach to investigating the near-surface structures through the use of the electromagnetic sounding. The advantages of the electro-magnetic sounding method and the problems of the nearssurface investigation and their solutions are described. Actual examples from the southwestern Takelamagan, western Qaidam and northern Xinjiang are taken to demonstrate the results and the capability of this approach in solving the nearsurface problems. It is also pointed out that the new approach could become both the basis for designing seismic acquisition parameters and determining the seismic shot locations,as well as supplying near-surface velocity models for seismic data processing so as to improve the quality of seismic sections. 相似文献
2.
Control devices incorporated with shape memory alloy 总被引：1，自引：1，他引：1
Shape Memory Alloy (SMA) is a type of material that offers some unique characteristics for use in devices for vibration control applications. Based on SMA's material properties, four types of control devices that incorporate NiTi SMA wires are introduced in this paper, which include three types of dampers (SMA damper, SMA-MR damper and SMA-friction damper) and one kind of isolation bearing (SMA-rubber bearing). Mechanical models of these devices and their experimental verifications are presented. To investigate the control performance of these devices, the SMA-MR damper and SMA-rubber bearing are applied to structures. The results show that the control devices could be effective in reducing the seismic response of structures. 相似文献
3.
《中国科学:地球科学(英文版)》2015,(6)
We present a comparative study of the most advanced three-dimensional time-dependent numerical simulation models of solar wind. These models can be classified into two categories:(I) theoretical, empirical and numerically based models and(II) self-consistent multi-dimensional numerical magnetohydrodynamic(MHD) models. The models of Category I are used to separately describe the solar wind solution in two plasma flows regions: transonic/trans-Alfvénic and supersonic/super-Alfvénic, respectively. Models of Category II construct a complete, single, numerical solar wind solution through subsonic/sub-Alfvénic region into supersonic/super-Alfvénic region. The Wang-Sheeley-Arge(WSA)/ENLIL in CISM is the most successful space weather model that belongs to Category I, and the Block-Adaptive-Tree-Solarwind-Roe-Upwind-Scheme(BATS-R-US) code in SWMF(Space Weather Modeling Framework) and the solar-interplanetary conservative element solution element MHD(SIP-CESE MHD) model in SWIM(Space Weather Integrated Model) are the most commonly-used models that belong to Category II. We review the structures of their frameworks, the main results for solar wind background studies that are essential for solar transient event studies, and discuss the common features and differences between these two categories of solar wind models. Finally, we conclude that the transition of these two categories of models to operational use depends on the availability of computational resources at reasonable cost and point out that the models' prediction capabilities may be improved by employing finer computational grids, incorporating more observational data and by adding more physical constraints to the models. 相似文献
4.
Characteristics of response spectra for long-periods of main-shock recordings of the Chi-Chi earthquake 总被引：1，自引：0，他引：1
Current practice uses predictive models to extrapolate long-period response spectra based on far-field recordings in moderate and weak earthquakes. However, the spectra are not long enough and the data are often not reliable, which means that the seismic design code cannot accurately define seismic design requirements for long-period structures. The near-field recordings in the main-shock of the Chi-Chi earthquake have a large signal-to-noise ratio (SNR), which makes them suitable for studying the long-period acceleration response spectrum up to 20 sec. The acceleration response spectra from 246 stations within 120 km of the causative fault are statistically analyzed in this paper. The influence of distance and site conditions on long-period response spectrum is discussed, and the shapes of the amplification spectra are compared with the standard spectra specified in the seismic design code of China. Finally, suggestions for future revisions to the code are proposed. 相似文献
5.
This paper refers to the CNOP-related algorithms and formulates the practical method and forecast techniques of extracting predictable components in a numerical model for predictable components on extended-range scales.Model variables are divided into predictable components and unpredictable chaotic components from the angle of model prediction error growth.The predictable components are defined as those with a slow error growth at a given range.A targeted numerical model for predictable components is established based on the operational dynamical extended-range forecast(DERF)model of the National Climate Center.At the same time,useful information in historical data are combined to find the fields for predictable components in the numerical model that are similar to those for the predictable components in historical data,reducing the variable dimensions in a similar judgment process and further correcting prediction errors of predictable components.Historical data is used to obtain the expected value and variance of the chaotic components through the ensemble forecast method.The numerical experiment results show that this method can effectively improve the forecast skill of the atmospheric circulation field in the 10–30 days extended-range numerical model and has good prospects for operational applications. 相似文献
6.
In the study of the application of MODIS satellite remote sensing data to earthquake prediction, the paper puts forward for the first time a quantitative method to estimate the ratio for the pixels with abnormal brightness temperature (BT) increase and a preliminary scheme for cloud removal. The principle is that, firstly, the cloudless data observed by the same satellite at the same period of time but in different days (usually 1 day to 3 days) are mosaiced to get high ratio of clear sky, and then the BT variation curve and mean square difference (MSD) of each pixel are calculated with the data from the covered area to determine daily whether the BT data of the day is normal or not at a certain pixel by using double the MSD as the criterion. The ratio for the pixels with abnormal BT increase can be calculated by dividing the total number of abnormal pixels with the total pixels of the whole area. Analysis on a series of recent earthquakes in the Taiwan area shows that the ratio for pixels with abnormal BT increase, which normally undulates around zero, has a sudden enhancement 1 day to 20 days before medium-strong earthquakes. It is expected that a new method for identifying earthquake auspice could be found through special studies in regions with frequent seismic activity by analyzing the change of the ratio for the pixels with abnormal BT increase from MODIS satellite remote sensing infrared (IR) information from which the effect of clouds has been removed to a certain extent. 相似文献
7.
R.Rana T.T.Soong 《地震工程与工程振动(英文版)》2004,3(1):85-100
A dual isolation problem for rotating machines consists of isolation of housing structures from the machinevi brations and protection of machines during an earthquake to maintain their functionality. Desirable characteristics of machine mounts for the above two purposes can differ significantly due to difference in nature of the excitation and performance criteria in the two situations. In this paper, relevant response quantities are identified that may be used to quantify performance and simplified models of rotating machines are presented using which these relevant response quantities may be calculated. Using random vibration approach with a stationary excitation, it is shown that significant improvement in seismic performance is achievable by proper mount design. Results of shaking table experiments performed with a realistic setup using a centrifugal pump are presented. It is concluded that a solution to this dual isolation problem lies in a semi-active mount capable of switching its properties from ‘operation-optimum’ to ‘seismic-optimum’ at the onset of a seismic event. 相似文献
8.
Abutment behavior significantly influences the seismic response of certain bridge structures. Specifically in the case of short bridges with relatively stiff superstructures typical of highway overpasses, embankment mobilization and inelastic behavior of the soil material under high shear deformation levels dominate the response of the bridge and its column bents. This paper investigates the sensitivity of bridge seismic response with respect to three different abutment modeling approaches. The abutment modeling approaches are based on three increasing levels of complexity that attempt to capture the critical components and modes of abutment response without the need to generate continuum models of the embankment, approach, and abutment foundations. Six existing reinforced concrete bridge structures, typical of Ordinary Bridges in California, are selected for the analysis. Nonlinear models of the bridges are developed in OpenSees. Three abutment model types of increasing complexity are developed for each bridge, denoted as roller, simplified, and spring abutments. The roller model contains only single-point constraints. The spring model contains discrete representations of backfill, bearing pad, shear key, and back wall behavior. The simplified model is a compromise between the efficient roller model and the comprehensive spring model. Modal, pushover, and nonlinear dynamic time history analyses are conducted for the six bridges using the three abutment models for each bridge. Comparisons of the analysis results show major differences in mode shapes and periods, ultimate base shear strength, as well as peak displacements of the column top obtained due to dynamic excitation. The adequacy of the three abutment models used in the study to realistically represent all major resistance mechanisms and components of the abutments, including an accurate estimation of their mass, stiffness, and nonlinear hysteretic behavior, is evaluated. Recommendations for abutment modeling are made. 相似文献
9.
In-situ cosmogenic nuclide s are receiving growing attention in surface Earth system science in which the steady-state denudation is an important assumption for estimating the surface denudation of long-lived(103-106 years)surfaces.However,distinguishing steady-state denudation and deciphering a reliable denudation rate from non-steady state denudation region are difficult.Recent depth profile models for investigating the denudation rate,exposure age and inheritance are widely used for sediment and regolith of steady-state denudation region.Here we present in-situ co smogenic nuclides10Be and26Al from two typical granite regolithes from Jixian in Tianjin and Tengchong in Yunnan to model non-steady landscape evolution process by using steady state(Model 1)and non-steady state(Model 2,continuous exposure;Model 3 a,changed denudation rate;Model 3 b,abrupt denudation event)models.The results of steady state model show that both regolithes are in non-steady state.10Be non-steady state models of Jixian regolith reveal that the surface has likely experienced a denudation rate change or an abrupt denudation event during the past several millennia,resulting in a non-steady state.The similar Model 3 a and 3 b denudation rates of 14.6-12.9+9.4and 14.7-14.7+9.0mmkyr-1,respectively,might demonstrate the long-term denudation rate rather than the exaggerated rate s of 39.0-2.3+2.6and 39.0-2.4+2.5mm kyr-1calculated by assuming steady-state denudation and ignoring inheritance.The non-steady state model results of Tengchong regolith suggest that the surface has likely experienced a strong denudation about 157 ka(10Be)or 127 ka(26Al)ago.This timing is basically consistent with the termination of the MIS 6(TII:130 ka)and the climate change events in the Tibetan Plateau,suggesting a strong surface landscape denudation during the transition from glacial to interglacial.The compiling of basin-wide denudation rates in the Tibetan Plateau shows a good positive correlation with the regional tectonic activity,indicating that the denudation rate derived from non-steady state region with strong tectonic activity is likely to be overestimated by assuming steady state.We suggest that a combination of steady state and non-steady state depth profile models should be used to quantify denudation rate and exposure age more accurately and effectively in strong tectonic activity or climate change regions. 相似文献
10.
《国际泥沙研究》2016,(2):139-148
Applications of sediment transport and water flow characteristics based sediment transport simulation models for a river system are presented in this study. An existing water–sediment model and a new sediment–water model are used to formulate the simulation models representing water and sediment movement in a river system. The sediment–water model parameters account for water flow characteristics embodying sediment transport properties of a section. The models are revised formulations of the multiple water inflows model describing water movement through a river system as given by the Muskingum principle. The models are applied to a river system in Mississippi River basin to estimate downstream sediment concentration, sediment discharge, and water discharge. River system and the river section parameters are estimated using a revised and the original multiple water inflows models by applying the genetic algorithm. The models estimate downstream sediment transport rates on the basis of upstream sediment/water flow rates to a system. Model performance is evaluated by using standard statistical criteria;downstream water discharge resulting from the original multiple water inflows model using the estimated river system parameters indicate that the revised models satisfactorily describe water movement through a river system. Results obtained in the study demonstrate the applicability of the sediment transport and water flow characteristics-based simulation models in predicting downstream sediment transport and water flow rates in a river system. 相似文献
11.
Input determination has a great influence on the performance of artificial neural network (ANN) rainfall–runoff models. To improve the performance of ANN models, a systematic approach to the input determination for ANN models is proposed. In the proposed approach, the irrelevant inputs are removed. Then an adequate ANN model, which only includes highly relevant inputs, is constructed. Unlike the trial‐and‐error procedure, the proposed approach is more systematic and avoids unnecessary trials. To demonstrate the effectiveness of the proposed approach, an application to actual typhoon events is presented. The results show that the proposed ANN model, which is constructed by the proposed approach, has advantages over those obtained by the trial‐and‐error procedure. The proposed ANN model has a simpler architecture, needs less training time, and performs better. The proposed ANN model is recommended as an alternative to existing rainfall–runoff ANN models. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
12.
Several statistical postprocessing methods are applied to results from a numerical weather prediction (NWP) model to test the potential for increasing the accuracy of its local precipitation forecasts. Categorical (Yes/No) forecasts for 12hr precipitation sums equalling or exceeding 0.1, 2.0 and 5.0 mm are selected for improvement. The two 12hr periods 0600-1800 UTC and 1800-0600 UTC are treated separately based on NWP model initial times 0000 UTC and 1200 UTC, respectively. Input data are taken from three successive summer seasons, April-September, 1994-96. The forecasts are prepared and verified for five synoptic stations, four located in the western Czech Republic, and one in Germany near the Czech-German border.
Two approaches to statistical postprocessing are tested. The first uses Model Output Statistics (MOS) and the second modifies the MOS approach by applying a successive learning technique (SLT). For each approach several statistical models for the relationship between NWP model predictors and predictand were studied. An independent data set is used for forecast verification with the skill measured by a True Skill Score.
The results of the statistical postprocessing are compared with the direct model precipitation forecasts from gridpoints nearest the stations, and they show that both postprocessing approaches provide substantially better forecasts than the direct NWP model output. The relative improvement increases with increasing precipitation amount and there is no significant difference in performance between the two 12hr periods. The skill of the SLT does not depend significantly on the size of the initial learning sample, but its results are nevertheless comparable with the results obtained from the MOS approach, which requires larger developmental samples. 相似文献
13.
Ahmet Güllü Ercan Yüksel Cem Yalçın A. Anıl Dindar Hasan Özkaynak Oral Büyüköztürk 《地震工程与结构动力学》2019,48(1):27-45
Input energy is the principal component of the energy balance equation. It is beneficial to determine, through its components, how the recoverable and irrecoverable energies are distributed within the structural elements. Several equations and attenuation relations to define mass-normalized input energy spectra exist in the literature. They are mainly proposed for elastic systems subjected to far-fault EQs. There is a lack of experimental verification of these proposed spectra. In this paper, experimental assessment was performed to the existing spectra, and further improvements were accomplished. For this purpose, steel cantilever columns were tested on the shake table for two specific historical EQs coincidently having similar spectral acceleration values. Based on the experimental results, a three-part mass-normalized relative input energy spectrum was formulated including soil type, EQ (corner period, intensity, duration, spectral acceleration, and velocity), and structural behavioral characteristics (period and structural damping). The proposed input energy spectrum was experimentally calibrated and numerically validated for various EQs featuring near- and far-field types. Analytical and experimental comparisons were made between the previously developed spectrum and the newly proposed one. The validation studies and the statistical evaluations exposed that the proposed spectrum yielded better agreement with the experimental and numerical results. 相似文献
14.
Discrete-fracture and dual-porosity models are infrequently used to simulate solute transport through fractured unconsolidated deposits, despite their more common application in fractured rock where distinct flow regimes are hypothesized. In this study, we apply four fracture transport models--the mobile-immobile model (MIM), parallel-plate discrete-fracture model (PDFM), and stochastic and deterministic discrete-fracture models (DFMs)--to demonstrate their utility for simulating solute transport through fractured till. Model results were compared to breakthrough curves (BTCs) for the conservative tracers potassium bromide (KBr), pentafluorobenzoic acid (PFBA), and 1,4-piperazinediethanesulfonic acid (PIPES) in a large-diameter column of fractured till. Input parameters were determined from independent field and laboratory methods. Predictions of Br BTCs were not significantly different among models; however, the stochastic and deterministic DFMs were more accurate than the MIM or PDFM when predicting PFBA and PIPES BTCs. DFMs may be more applicable than the MIM for tracers with small effective diffusion coefficients (De) or for short timescales due to differences in how these models simulate diffusion or incorporate heterogeneities by their fracture networks. At large scales of investigation, the more computationally efficient MIM and PDFM may be more practical to implement than the three-dimensional DFMs, or a combination of model approaches could be employed. Regardless of the modeling approach used, fractures should be incorporated routinely into solute transport models in glaciated terrain. 相似文献
15.
In recent decades,a few Godunov-type,finite volume two-dimensional(2D)unstructured grid,coupled flow,and sediment models(GF2DUCM)have been developed for flows over erodible beds.These kinds of models are generally analyzed as a Vertex Model(VM)that define topography at the cell vertex,which can lead to the non-conservation of mass regarding flow,sediment,and bed evolution.Here,a full cellcantered variable storage method(Central Model or CM)is applied as the solution of the GF2DUCM.In this method,terrain elevation is defined at the cell centroids;this accurately describes the physical relations between the water depth and topography deformation.This approach can fully eliminate calculation errors in topography deformation at local cells caused by the interpolation of topography deformation at the cell vertex,and reduced uncertainty in the computation of the GF2DUCM.The model performance is systematically tested using a series of laboratory experiments,which demonstrate the mass conservation feature and high accuracy in reproducing hydrodynamic and morphological processes. 相似文献
16.
通过对3个足尺性能增强再生混凝土框架中节点进行低周反复加载试验，按照传统延性损伤模型（单参数）、改进的Park-Ang损伤模型（双参数）对其损伤演化与累积进行分析:各试件特征位移等于20 mm时，试件已经出现损伤，但按照延性损伤模型计算结果为负；当特征位移超过100 mm时，改进的Park-Ang损伤模型计算结果表明各试件已经完全破坏，无法继续承载，但试件实际结果却仍表现出一定的承载能力与耗能能力。因而有必要对前述损伤模型进行修正，使其能够适用于性能增强再生混凝土结构之中。基于前述试验结果，针对改进的Park-Ang损伤模型，提出并拟合了纤维项系数、位移项系数和能量项系数3种修正系数，并建立了相应的修正的Park-Ang损伤模型。最后，利用所提出的损伤模型，以HF-RAC2为例进行了损伤指标误差分析，结果表明:平均误差在6%以内，即:所提出双参数损伤模型能够应用于性能增强再生混凝土框架节点地震损伤与评估分析之中。 相似文献
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18.
为满足流域防洪规划工作的需要,针对鄱阳湖湖区暴雨洪水特点,分别用面积比拟法,修正总入流法,单水源模型（现预报方案）,新安江三水源模型,对湖区４个实际大水年份进行分析计算．在新安江三水源模型中分析了鄱阳湖高低水位时水陆面积变化对产汇流的影响,并给出了相应的计算公式．结果表明,复杂的概念性降雨径流模型能充分地模拟径流洪水过程;而在合理的条件下,运用简单的方法亦能取得较好的效果,通过比较分析,提出鄱阳湖 相似文献
19.
Information on snow properties plays an important role in hydrological, meteorological and climatological applications. Passive microwave remote sensing is an effective method to retrieve snowpack parameters; however, the observations can be obscured if there is wet snow in the satellite footprint. To study the emission properties of wet snow and check its response to snow wetness, this paper applies the multi‐layer Helsinki University of Technology (HUT) snow emission model coupled with the Advanced Integral Equation Model to simulate the low‐wetness snowpack observed at Luancheng in November 2009, and the high wetness snowpack observed at Weissfluhjoch in June 1995. Input parameters are acquired by the in‐situ snow pit measurements, while the snow grain size is fitted by comparing model predictions with the observed passive microwave signals at a range of observing angles. Results show that the application of a multi‐layer model is capable to consider the distribution pattern of the snow wetness along the snow profile and the refrozen ice crust of the snow surface. The multi‐layer HUT model is able to reproduce the wet snow emission properties, with an rms error of 4.4 K (at Luancheng) and 5.7 K (at Weissfluhjoch) at vertical polarization, and an rms error of 7.9 K (at Luancheng) and 11.4 K (at Weissfluhjoch) at horizontal polarization. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
20.
Helena Mouriño Maria Isabel Barão 《Stochastic Environmental Research and Risk Assessment (SERRA)》2010,24(4):499-511
In this paper we consider a Linear Regression Model with a design matrix that fits the periodic structure of a time series.
As a consequence, the residuals are very often autocorrelated. The main problem is that residual autocorrelation does not
necessarily entail error autocorrelation. To analyse the effects of selecting different formulations to accommodate the autocorrelation
in the residuals, we consider two seemingly different ways to deal with this problem: the Linear Regression Model with the
error terms following an Autoregressive Stationary Process and the Partial Adjustment Model. We study the equivalence between
the two formulations. We go over the problem of estimating the parameters and, especially, of making inferences in this framework.
After parameter estimation, we analyse the adequacy of the models. We demonstrate that the issue of selecting the most appropriate
model to capture the autocorrelation in the residuals is, in this context, a kind of an artefact since the main results concerning
the fitted values and forecasting features are the same. These modelling procedures are applied to the Portuguese coastal
upwelling data and we compare the estimated models. 相似文献