Damping in tall buildings—a mechanism and a predictor

Only when the data base is of sufficient quality can a theoretical model of any process be justified. Such a data base has recently been assembled in the field of damping in tall buildings. It is now possible to specify a damping value appropriate to a particular building vibrating at a specified amplitude which is well correlated with values which are measured in practice. The mechanism on which this predictor is based suggests that the predictor will be applicable to other types of structure as well. As yet the data base for these other structures does not exist, but some circumstantial evidence is encouraging.     

Forecasting the energy produced by a windmill on a yearly basis

The objective of this article is to study as extensively as possible the uncertainties affecting the annual energy produced by a windmill. In the literature, the general approach is to estimate the mean annual energy from a transformation of a Weibull distribution law. Then the issue is reduced to estimating the coefficients of this distribution. This is obtained by classical statistical methods. Therefore, the uncertainties are mostly limited to those resulting from the statistical procedures. But in fact, the real uncertainty of the random variable which represents the annual energy cannot been reduced to the uncertainty on its mean and to the uncertainties induced from the estimation procedure. We propose here a model, which takes advantage of the fact that the annual energy production is the sum of many random variables representing the 10?min energy production during the year. Under some assumptions, we make use of the central limit theorem and show that an intrinsic uncertainties of wind power, usually not considered, carries an important risk. We also explain an observation coming from practice that the forecasted annual production is always overestimated, which creates a risk of reducing the profitability of the operation.     

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.     

On magneto-elastic disturbaces in a visco-elastic cylinder placed in a magnetic field

Summary The present note is an attempt to discuss the disturbances in a cylinder characterised by a visco-elasticity of general linear type, which is subjected to a magnetic field.     

Barotropic instability of a boundary jet on a sloping bottom

Abstract

The stability of a shear flow on a sloping bottom in a homogeneous, rotating system was investigated by means of a laboratory experiment.

The basic flow was driven near a vertical wall of a circular container by a ring-shaped plate that contacted with a free surface of the working fluid and rotated relative to the fluid container. The velocity profile was asymmetric in the radial direction and had only one inflection point. The velocity profile was well expressed by a linear theory for the vertical shear layer.

The effect of the circular geometry was checked by comparing experimental results obtained in two fluid systems in which only the sign of the curvature was opposite and it was confirmed that circular geometry was not essential for the shear flow on the sloping bottom in this experiment.

It was found that the sloping bottom stabilizes the basic flow only when the drift direction of the topographic Rossby wave is opposite to that of the basic flow. The viscous dissipation in both the Ekman layer and the interior region was also important in determining the critical Rossby number.

The eddy fields caused by the instability can be classified into two types: One is the stationary eddy field in which a row of eddies moves along the basic flow without changing form. The other is the flow pattern in which eddies have finite life times and their configuration is not well organized. When the sloping bottom does not stabilize the basic flow, the former flow pattern is realized, otherwise the latter flow pattern appears.

The wave numbers of the eddies in the regular flow pattern were observed as a function of the Rossby number. The relation did not fit to linear preferred modes predicted by an eigenvalue problem.     

Deterministic and stochastic analyses of a nonlinear system with a Biot visco‐elastic element

In the paper the Biot hysteretic model involving an infinite collection of elements whose dynamic characteristics are specified through a probability density‐like function is re‐examined; in the limit case, the Biot model yields a dynamic system with ideal hysteretic damping which is known to be problematic for random vibration analysis. It is shown that bona fide Monte Carlo simulations can be conducted for the Biot model by treating, cautiously, the integrodifferential equation which is involved; this is based on recursive calculations of double integrals encountered in the representation of the system dynamics. The numerical results which pertain to the Monte Carlo studies are further used to assess the accuracy of a statistical linearization procedure adopted in determining the response of the hysteretically damped system to white noise. Published in 2001 by John Wiley & Sons, Ltd.     

Empirical relationships for estimating stream depletion by a well pumping near a gaining stream

Siting wells near streams requires an accurate estimate of the quantity of water derived from the river due to pumping. A number of hydrogeological and hydraulic parameters influence this value. This study estimates stream depletion under steady-state conditions for a variety of hydrogeological systems. A finite differences model was used to analyze several hydrogeological situations, and for each of these the stream depletion was estimated using an advective transport method. An empirical equation for stream depletion was obtained for the case of a stream that partially penetrates the aquifer and a pumping well that is screened over a portion of the aquifer. The derived equation, which is valid for both isotropic and anisotropic conditions, expresses stream depletion as a function of the unit inflow to the river, the discharge of the pumping well, the well screen length, the distance between the river and pumping well, the wetted perimeter, and a new parameter called "overlap," which is defined to be the distance between the riverbed and the top of well screen. The overlap parameter makes it possible to consider indirectly the vertical component of flow, which is accentuated when the well is screened below the streambed. The formula proposed here should be useful in deciding where to locate a pumping well and to decide the appropriate length of its screen.     

Dynamic Rupture in a 3-D Particle-based Simulation of a Rough Planar Fault

An appreciation of the physical mechanisms which cause observed seismicity complexity is fundamental to the understanding of the temporal behaviour of faults and single slip events. Numerical simulation of fault slip can provide insights into fault processes by allowing exploration of parameter spaces which influence microscopic and macroscopic physics of processes which may lead towards an answer to those questions. Particle-based models such as the Lattice Solid Model have been used previously for the simulation of stick-slip dynamics of faults, although mainly in two dimensions. Recent increases in the power of computers and the ability to use the power of parallel computer systems have made it possible to extend particle-based fault simulations to three dimensions. In this paper a particle-based numerical model of a rough planar fault embedded between two elastic blocks in three dimensions is presented. A very simple friction law without any rate dependency and no spatial heterogeneity in the intrinsic coefficient of friction is used in the model. To simulate earthquake dynamics the model is sheared in a direction parallel to the fault plane with a constant velocity at the driving edges. Spontaneous slip occurs on the fault when the shear stress is large enough to overcome the frictional forces on the fault. Slip events with a wide range of event sizes are observed. Investigation of the temporal evolution and spatial distribution of slip during each event shows a high degree of variability between the events. In some of the larger events highly complex slip patterns are observed.     

Reflection from a deep interface in a strongly heterogeneous layered medium1

We consider the problem of acoustic pulse propagation through a layered medium with a reflector at one end. The fluctuations in the medium properties are assumed to be strong, i.e. of finite amplitude, rapid in comparison to the typical wavelength and to have statistical structure. The depth of the reflector is assumed to be large in comparison to the wavelength. In this regime, simple formulae for the reflected pulse and its arrival time at the surface are obtained. The amplitude of the pulse is broadened and attenuated as a result of multiple scattering: the fine-layered structure of the medium can be characterized by a single constant which appears in the formula for the limiting waveform and which measures the size of the fluctuations in the medium. Within the theory, the commonly observed discrepancy between the integrated sonic traveltime and the seismic traveltime can be studied and understood. The theory is a natural extension of the long-wavelength effective medium theory of Backus. The analysis is rigorous and based on the invariant embedding technique.     

Similarity solution for capillary redistribution of two phases in a porous medium with a single discontinuity

In this paper we consider one-dimensional capillary redistribution of two immiscible and incompressible fluids in a porous medium with a single discontinuity. We study a special time-dependent solution, a similarity solution, which is found when the initial saturation is discontinuous at the same point as the permeability and porosity, and is constant elsewhere. The similarity solution can be used to validate numerical algorithms describing two-phase flow in porous media with discontinuous heterogeneities. We discuss the construction of the similarity solution, in which we pay special attention to the interface conditions at the discontinuity, both for media with positive and zero entry pressure. Moreover, we discuss some qualitative properties of the solution, and outline a numerical procedure to determine its graph. Examples are given for the Brooks-Corey and Van Genuchten model. We also consider similarity solutions for unsaturated water flow, which is a limit case of two-phase flow for negligible nonwetting phase viscosity.     

Dynamic behavior of a smart device on a surface subjected to earthquake motion

This paper leverages concepts from an existing model to simulate the planar response of a smart device subjected to friction forces induced by an underlying moving plane. An interpolation technique is used to enhance detection of transition points (between sticking and sliding states), which must be accurately identified because of the frequency of their occurrence during seismic motion. The behavior of a smart device on an unconstrained table or desk, which is itself on a moving floor, is introduced and discussed. After validation of the results using experimental data, the revised model is used to study the sliding potential of smart devices on a surface during strong seismic events. Sliding spectra associated with selected ground motions are presented and extended to incorporate the effect of vertical accelerations with the purpose of assessing their influence. It is shown that vertical accelerations have a minimal effect on the sliding behavior of smart devices and that a “probability of exceeding the slip limit” curve can be developed to relate the probability of sticking to a demand parameter that represents the ground motion.     

Motion in a non-homogeneous elastic medium by a twisting impulsive force on the surface of a spherical cavity

Summary In this paper, the propagation of disturbance due to a twisting impulsive force on the surface of a spherical cavity, in a non-homogeneous isotropic medium, in which the rigidity and density vary inversely as the distance from the centre is investigated. Numerical solution is done by the method suggested byKromm.     

SH波作用下浅埋裂纹附近半圆形凸起的地震动

利用Green函数、复变函数及多极坐标法研究了浅埋裂纹附近的半圆形凸起地形对SH波的散射问题。首先求解出适合本问题的Green函数,即含有半圆形凸起的弹性半空间内任意一点承受时间谐和的出平面线源荷载作用时位移场的解答。然后,从半圆形凸起地形对SH波的散射问题出发,利用本问题的Green函数在基体内构造裂纹。最后给出了浅埋裂纹附近的半圆形凸起地形对SH波散射的位移场。通过算例讨论了裂纹对地表位移幅值的影响,结果表明裂纹在一定情况下具有减震作用。     

Torsional vibration of a finite cylindrical cavity in a two-layer transversely isotropic half-space

The aim of this paper is to present a rigorous investigation for a two-layered transversely isotropic linear elastic half-space containing a circular cylindrical cavity of length equal to the top layer undergoing mono-harmonic ring shape shear stress applied either on the vertical cylindrical surface or on the base of the cavity. To this end, a combination of Fourier cosine integral transform for depth and Hankel integral transform for radial distance are used, which translate the boundary value problem to a singular integral equation for the shear stress comes out from the continuity of two layers. The integral equation is solved for some collocation points with a smoothed variable of distance, which is adapted with the use of a free parameter. It is shown that, although the shear stress is highly singular, it does not highly depend on this free parameter. Both the analytical and numerical results are verified with both the static isotropic and dynamic transversely isotropic homogeneous cases. In addition, some new graphical results are presented for more understanding in engineering point of view.     

Ground penetrating radar sounding of a temperate glacier; modelling of a multilayered medium1

A numerical simulation of electromagnetic propagation through a multilayered medium is performed in order to explain and interpret the signal received from the radar sounding of a temperate glacier. During the winter of 1990, several radar profiles were obtained on the Mont-de-Lans glacier in the French Alps with a ground penetrating radar which uses a phase modulation of the transmitted pulse by coded sequences. The pulse compression is obtained by applying the matched filter to the received signal, which provides a range-resolution of about 8 m in the ice. The profiles recorded on the temperate glacier do not show a single clear reflection from the ice-bedrock interface, but they exhibit widely distributed energy decreasing with depth. This may be due to the inhomogeneous inner structure of the temperate glacier and we use a simple model of a layered medium to compute a simulation of the propagation. Thus, partial reflection at each layer and scattering from a rough basal interface may explain the observed signal. A computer-based technique is used to locate on the data the bottom of the glacier in order to estimate the ice thickness. The results from the different radar profiles are consistent and are a good fit to the thickness which has been determined by other geophysical methods.     

The evolving concept of a magnetospheric substorm

A magnetospheric substorm is an episode of energy transport and dissipation in the Earth|s ionosphere and mag- netosphere which takes place in response to a time limited increase in energy input from the solar wind to the magnetosphere. For the past few decades, scientists have tried to understand the physical processes which take place that are responsible for the substorm disturbances of the geospace environment. In this paper, The development of the substorm concept is reviewed from its origins at the beginning of the 20th century to the present time. The theoretical framework in which substorm physics is normally presented is then discussed, and an outline is given of how that framework has changed in recent times. This paper concludes by posing two questions which need to be answered if further progress is to be made in solving the substorm problem.     

Contamination of a well in a uniform background flow

In this paper we describe the transport of pollution in groundwater in the neighbourhood of a well in a uniform background flow. We compute the rate at which contaminated particles reach the well as a function of the place of the source of pollution. The motion of a particle in a dispersive flow is seen as a random walk process. The Fokker-Planck equation for the random motion of a particle is transformed using the complex potential for the advective flow field. The resulting equation is solved asymptotically after a stretching transformation. Finally, the analytical solution is compared with results from Monte Carlo simulations with the random walk model. The method can be extended to arbitrary flow fields. Then by a numerical coordinate transformation the analytical results can still be employed.     

Static deformation of a multilayered half-space by a very long strike-slip fault

Summary The formulas for the elastic residual field of a very long strike-slip fault in a multilayered elastic half-space are given. It is assumed that the medium is made up ofn parallel, isotropic and homogeneous layers lying over an isotropic, homogeneous half-space and being in welded contact. The formulas which allow the calculation of the displacement and stress fields due to an arbitrary very long strike-slip fault are derived. The explicit expressions of coefficients which appear in these formulas are listed for the casesn=1 andn=2.     

The research of a solution on locating optimally a station for seismic disasters rescue in a city

ＴｈｅｒｅｓｅａｒｃｈｏｆａｓｏｌｕｔｉｏｎｏｎｌｏｃａｔｉｎｇｏｐｔｉｍａｌｌｙａｓｔａｔｉｏｎｆｏｒｓｅｉｓｍｉｃｄｉｓａｓｔｅｒｓｒｅｓｃｕｅｉｎａｃｉｔｙＱｉｎｇ－ＬｉｎＹＡＯ（姚清林）（ＩｎｓｔｉｔｕｔｅｏｆＧｅｏｌｏｇｙ，ＳｔａｔｅＳｅｉ...     

Steady-state response of a stratified half-space subjected to a horizontal arbitrary buried uniform load applied at a circular area

This paper outlines a method of analysis of the steady-state dynamic response of a stratified soil to a horizontal time-harmonic loading applied at a circular area. It is assumed the load to be uniformly distributed over the contact area and embedded at an arbitrary depth. It is shown that by means of application of integral Hankel transform, the problem can be reduced to a form of a single integral, which can be taken numerically. Results of the numerical simulations for an embedded horizontal impulse load are presented to demonstrate the efficiency of the developed procedure.