Numerical Modelling Investigation of Wave Interaction on Composite Berm Breakwater

China Ocean Engineering - The breakwaters have experienced many changes during their construction history. These changes have been considered to improve their performance, depending on their...     

Instabilities in a nonstationary model of self-gravitating disks. II. Warp modes of vertical oscillations

Gravitational instabilities with respect to warp modes of vertical oscillations are examined for nonlinearly nonequilibrium disk models with isotropic and anisotropic velocity diagrams. Nonstationary analogs of the dispersion relations for vertical oscillations in these models are derived in a general form. A detailed study is made of the major large scale oscillatory modes, which correspond primarily to the most common type of warp in the form of an integral sign, as well as to dome-shaped, U-shaped, and precessional warps. Critical diagrams showing the initial virial relation as a function of the rotation parameter for the nonstationary model are constructed for each of these vertical oscillation modes. A comparative analysis is made of the growth rates of the instabilities for these modes in order to determine the dependence of the characteristic times for their appearance on the basic physical parameters of the two models.     

Accelerated expansion of the universe in a non-trivial extra-dimensional topology

The recent observational available data for an accelerated expansion state of the present universe, obtained from distant SNeIa gave strong support to the search of alternative cosmologies. Recently, there have been a number of different attempts to modify Einstein’s gravity to yield accelerated expansion at late times. Unfortunately, many of the theoretical models discussed in the literature are plagued with theoretical problems, in particular the singularity problem at the origin of time. In the present work we have analyzed a multidimensional spacetime Friedmann–Robertson–Walker (FRW) model with a decaying cosmological constant and a varying gravitational constant. Many interesting consequences are revealed, in particular the behavior of the scale factor and the shape of the universe in terms of the number of extra dimensions.     

Comparison of dynamic stiffnesses of rigid square and rectangular foundations by DBEM and IBEM

In this work, the Direct and Indirect Boundary Element Methods as applied to dynamic soil structure interaction problems, are compared. Both the methods are used to find the dynamic stiffnesses of rigid surface and embedded foundations. For surface foundations, the results obtained by the two methods were very close for the frequency range considered, but for embedded foundations at higher frequencies, the Indirect Boundary Element Method produced erroneous values for the real part of vertical compliance. The possible reasons for this discrepancy are also studied in this paper.     

Définition de la perméabilité équivalente des massifs fracturés par des méthodes d'homogénéisationDefinition of the permeability of fractured rock masses by homogenisation methods

In the methods used for determination of the hydraulic behaviour at large scale of fractured rock masses, based on the simulation of flow in a fracture network, the mean flux and the mean pressure gradient in the network are not rigorously determined. A method is given for deriving these quantities, in a heterogeneous permeable block, from pressure and flux values on the boundary of the block. A block conductivity tensor is then defined, based on the condition of linear variation of the pressure on the boundary of the block. It is shown that this conductivity tensor is symmetric and positive-definite. An example of application to a model of fractured medium is given. To cite this article: A. Pouya, A. Courtois, C. R. Geoscience 334 (2002) 975–979.     

Gravitational potential energy of a pair of overlapping galaxies

The interaction of the gravitational potential energy of a pair of overlapping Plummer-model galaxies is determined exactly for various separationsr of their centres. It is shown that the results can be well represented by the simple relationW(r)=–GM ₁ M ₂/(r ²+ ²)^1/2, where 1/ is the average reciprocal distance between the stars of two galaxies of massesM ₁ andM ₂ when they have zero separation.     

Microwave solar limb brightening

Previous models of microwave limb brightening have omitted the alignment of spicules along supergranule boundaries, have neglected the high temperature sheath around spicules, and have assumed an interspicular medium which was averaged over chromospheric network and non-network regions. We present a model which includes these factors. By constraining the model to conform to results from earlier UV and optical studies we are effectively left with two free parameters: the temperature at the core of the spicules, T _core, and (at solar minimum), the interspicular chromospheric network density model of the lower transition zone. The absence of limb brightening at the short millimeter wavelengths implies T _core 6000 k. Differences between the model and certain deconvolved observations near 9 mm are expected as a consequence of an extension of emission beyond the optical limb, predicted by the model, which affects the accuracy of the deconvolution technique. Unlike models which assume homogeneous spicules in a random distribution, ours does not require an abnormally high spicule area.     

Field investigation on the results of non-linear shallow water equations in the Swash Zone

For the study of the cross-shore wave-induced hydrodynamics in the swash zone, a numerical model is developed based on the one-dimensional non-linear shallow water (NSW) equations for prediction of hydrodynamic parameters in the swash zone. In order to evaluate the accuracy of the outputs of the numerical model, the model's predictions in terms of water surface elevations and cross-shore velocities, are compared to field data from full-scale experiments conducted on three sites with different beach slope; mild and steep, several bed particle sizes and under various incident wave conditions. The quantitative and qualitative comparison of the results of the numerical model and the full-scale data reveals that the model can generally predict many aspects of the flow in the surf and swash zone on both types of beach. The accuracy is adequate for application in a sediment transport study. Considering the time-history and probability distribution of water surface elevation, the model is generally more accurate on steep beaches than on the mild beach. The model can adequately simulate the dominant frequency across the beach and saturation of higher frequencies on both mild and steep beaches for various incident wave energy characteristics. With regard to the horizontal (cross-shore) velocity, the sawtooth shape of time-history and negative acceleration of water are well predicted by the model for both mild and steep beaches. Due to the uncertainties in maximum and minimum values of velocity data, clear judgement about the accuracy of the numerical model in this matter was not possible. However, the comparison of the minimum velocities (offshore direction) revealed that the application of friction factors below the range which is suggested by literature best match the data.     

COMPARISON OF HEAVY METAL CONCENTRATIONS IN SURFACE SEDIMENT OF TANJUNG PIAI WETLAND WITH OTHER SITES RECEIVING ANTHROPOGENIC INPUTS ALONG THE SOUTHWESTERN COAST OF PENINSULAR MALAYSIA

1 INTRODUCTIONOur sampling trip to Tanjung Piai wetland in2002 showed that the site had not been developed andrecognized yet as a wetland of international importance(Ramsar). Recently, our field trip in January 2005to the same site to collect sediment sam…     

Influence of earthquake ground motion incoherency on multi-support structures

A linear response history analysis method is used to determine the influence of three factors: geometric incoherency, wave-passage, and local site characteristics on the response of multi-support structures subjected to differential ground motions. A one-span frame and a reduced model of a 24-span bridge, located in Las Vegas, Nevada are studied, in which the influence of each of the three factors and their combinations are analyzed. It is revealed that the incoherency of earthquake ground motion can have a dramatic influence on structural response by modifying the dynamics response to uniform excitation and inducing pseudo-static response, which does not exist in structures subjected to uniform excitation. The total response when all three sources of ground motion incoherency are included is generally larger than that of uniform excitation.